drivers/tty/serial/kgdboc.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
From: LiuYe <liu.yeC@h3c.com>
Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
attempt to use schedule_work() to provoke a keyboard reset when
transitioning out of the debugger and back to normal operation.
This can cause deadlock because schedule_work() is not NMI-safe.
The stack trace below shows an example of the problem. In this
case the master cpu is not running from NMI but it has parked
the slave CPUs using an NMI and the parked CPUs is holding
spinlocks needed by schedule_work().
example:
BUG: spinlock lockup suspected on CPU#0, namex/10450
lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1
ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000
ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20
Call Trace:
[<ffffffff81479e6d>] ? __schedule+0x16d/0xac0
[<ffffffff8147a7fc>] ? schedule+0x3c/0x90
[<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120
[<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10
[<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0
[<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20
[<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0
[<ffffffff8108c540>] ? wake_up_q+0x70/0x70
[<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0
[<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75
CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1
Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019
0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000
ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980
000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0
Call Trace:
<#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2
[<ffffffff810a7f7f>] spin_dump+0x7f/0x100
[<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150
[<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20
[<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0
[<ffffffff8108c4c5>] wake_up_process+0x15/0x20
[<ffffffff8107b371>] insert_work+0x81/0xc0
[<ffffffff8107b4e5>] __queue_work+0x135/0x390
[<ffffffff8107b786>] queue_work_on+0x46/0x90
[<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70
[<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610
[<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0
[<ffffffff81054e21>] __kgdb_notify+0x71/0xd0
[<ffffffff81054eb5>] kgdb_notify+0x35/0x70
[<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70
[<ffffffff8108304d>] notify_die+0x3d/0x50
[<ffffffff81017219>] do_int3+0x89/0x120
[<ffffffff81480fb4>] int3+0x44/0x80
We fix the problem by using irq_work to call schedule_work()
instead of calling it directly. irq_work is an NMI-safe deferred work
framework that performs the requested work from a hardirq context
(usually an IPI but it can be timer interrupt on some
architectures).
Note that we still need to a workqueue since we cannot resync
the keyboard state from the hardirq context provided by irq_work.
That must be done from task context for the calls into the input
subystem. Hence we must defer the work twice. First to safely
switch from the debug trap (NMI-like context) to hardirq and
then, secondly, to get from hardirq to the system workqueue.
Signed-off-by: LiuYe <liu.yeC@h3c.com>
Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
V5 -> V6: Replace with a more professional and accurate answer.
V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
V3 -> V4: Add changelogs
V2 -> V3: Add description information
V1 -> V2: using irq_work to solve this properly.
---
---
drivers/tty/serial/kgdboc.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164..161b25ecc 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -22,6 +22,7 @@
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
+#include <linux/irq_work.h>
#define MAX_CONFIG_LEN 40
@@ -99,10 +100,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+ schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
static void kgdboc_restore_input(void)
{
if (likely(system_state == SYSTEM_RUNNING))
- schedule_work(&kgdboc_restore_input_work);
+ irq_work_queue(&kgdboc_restore_input_irq_work);
}
static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +141,7 @@ static void kgdboc_unregister_kbd(void)
i--;
}
}
+ irq_work_sync(&kgdboc_restore_input_irq_work);
flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
--
2.25.1On Tue, Mar 26, 2024 at 03:40:14PM +0800, liu.yec@h3c.com wrote:
> Note that we still need to a workqueue since we cannot resync
> the keyboard state from the hardirq context provided by irq_work.
I think you are missing a word between "to" and "a", right?
> That must be done from task context for the calls into the input
> subystem. Hence we must defer the work twice. First to safely
> switch from the debug trap (NMI-like context) to hardirq and
> then, secondly, to get from hardirq to the system workqueue.
>
> Signed-off-by: LiuYe <liu.yeC@h3c.com>
> Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
>
> ---
> V5 -> V6: Replace with a more professional and accurate answer.
> V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
> V3 -> V4: Add changelogs
> V2 -> V3: Add description information
> V1 -> V2: using irq_work to solve this properly.
> ---
> ---
> drivers/tty/serial/kgdboc.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 7ce7bb164..161b25ecc 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -22,6 +22,7 @@
> #include <linux/module.h>
> #include <linux/platform_device.h>
> #include <linux/serial_core.h>
> +#include <linux/irq_work.h>
>
> #define MAX_CONFIG_LEN 40
>
> @@ -99,10 +100,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
>
> static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
>
> +static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
> +{
> + schedule_work(&kgdboc_restore_input_work);
As this is a "two stage deferment" or something like that, it should be
documented in the code exactly why this is needed and what is happening,
otherwise it looks very odd.
thanks,
greg k-h
From: LiuYe <liu.yeC@h3c.com>
Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
attempt to use schedule_work() to provoke a keyboard reset when
transitioning out of the debugger and back to normal operation.
This can cause deadlock because schedule_work() is not NMI-safe.
The stack trace below shows an example of the problem. In this
case the master cpu is not running from NMI but it has parked
the slave CPUs using an NMI and the parked CPUs is holding
spinlocks needed by schedule_work().
example:
BUG: spinlock lockup suspected on CPU#0, namex/10450
lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1
ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000
ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20
Call Trace:
[<ffffffff81479e6d>] ? __schedule+0x16d/0xac0
[<ffffffff8147a7fc>] ? schedule+0x3c/0x90
[<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120
[<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10
[<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0
[<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20
[<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0
[<ffffffff8108c540>] ? wake_up_q+0x70/0x70
[<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0
[<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75
CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1
Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019
0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000
ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980
000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0
Call Trace:
<#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2
[<ffffffff810a7f7f>] spin_dump+0x7f/0x100
[<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150
[<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20
[<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0
[<ffffffff8108c4c5>] wake_up_process+0x15/0x20
[<ffffffff8107b371>] insert_work+0x81/0xc0
[<ffffffff8107b4e5>] __queue_work+0x135/0x390
[<ffffffff8107b786>] queue_work_on+0x46/0x90
[<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70
[<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610
[<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0
[<ffffffff81054e21>] __kgdb_notify+0x71/0xd0
[<ffffffff81054eb5>] kgdb_notify+0x35/0x70
[<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70
[<ffffffff8108304d>] notify_die+0x3d/0x50
[<ffffffff81017219>] do_int3+0x89/0x120
[<ffffffff81480fb4>] int3+0x44/0x80
We fix the problem by using irq_work to call schedule_work()
instead of calling it directly. irq_work is an NMI-safe deferred work
framework that performs the requested work from a hardirq context
(usually an IPI but it can be timer interrupt on some
architectures).
Note that we still need to a workqueue since we cannot resync
the keyboard state from the hardirq context provided by irq_work.
That must be done from task context for the calls into the input
subystem. Hence we must defer the work twice. First to safely
switch from the debug trap (NMI-like context) to hardirq and
then, secondly, to get from hardirq to the system workqueue.
Signed-off-by: LiuYe <liu.yeC@h3c.com>
Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
V6 -> V7: Add comments in the code.
V5 -> V6: Replace with a more professional and accurate answer.
V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
V3 -> V4: Add changelogs
V2 -> V3: Add description information
V1 -> V2: using irq_work to solve this properly.
---
---
drivers/tty/serial/kgdboc.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164..750ed66d2 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -22,6 +22,7 @@
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
+#include <linux/irq_work.h>
#define MAX_CONFIG_LEN 40
@@ -98,11 +99,29 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
}
static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
+/*
+ * We fix the problem by using irq_work to call schedule_work()
+ * instead of calling it directly. irq_work is an NMI-safe deferred work
+ * framework that performs the requested work from a hardirq context
+ * (usually an IPI but it can be timer interrupt on some
+ * architectures). Note that we still need to a workqueue since we cannot resync
+ * the keyboard state from the hardirq context provided by irq_work.
+ * That must be done from task context for the calls into the input
+ * subystem. Hence we must defer the work twice. First to safely
+ * switch from the debug trap (NMI-like context) to hardirq and
+ * then, secondly, to get from hardirq to the system workqueue.
+ */
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+ schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
static void kgdboc_restore_input(void)
{
if (likely(system_state == SYSTEM_RUNNING))
- schedule_work(&kgdboc_restore_input_work);
+ irq_work_queue(&kgdboc_restore_input_irq_work);
}
static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +152,7 @@ static void kgdboc_unregister_kbd(void)
i--;
}
}
+ irq_work_sync(&kgdboc_restore_input_irq_work);
flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
--
2.25.1On Tue, Mar 26, 2024 at 04:54:07PM +0800, liu.yec@h3c.com wrote:
> From: LiuYe <liu.yeC@h3c.com>
>
> Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
> attempt to use schedule_work() to provoke a keyboard reset when
> transitioning out of the debugger and back to normal operation.
> This can cause deadlock because schedule_work() is not NMI-safe.
>
> The stack trace below shows an example of the problem. In this
> case the master cpu is not running from NMI but it has parked
> the slave CPUs using an NMI and the parked CPUs is holding
> spinlocks needed by schedule_work().
>
> example:
> BUG: spinlock lockup suspected on CPU#0, namex/10450
> lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1
> ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000
> ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20
> Call Trace:
> [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0
> [<ffffffff8147a7fc>] ? schedule+0x3c/0x90
> [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120
> [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10
> [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0
> [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20
> [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0
> [<ffffffff8108c540>] ? wake_up_q+0x70/0x70
> [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0
> [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75
> CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1
> Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019
> 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000
> ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980
> 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0
> Call Trace:
> <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2
> [<ffffffff810a7f7f>] spin_dump+0x7f/0x100
> [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150
> [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20
> [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0
> [<ffffffff8108c4c5>] wake_up_process+0x15/0x20
> [<ffffffff8107b371>] insert_work+0x81/0xc0
> [<ffffffff8107b4e5>] __queue_work+0x135/0x390
> [<ffffffff8107b786>] queue_work_on+0x46/0x90
> [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70
> [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610
> [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0
> [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0
> [<ffffffff81054eb5>] kgdb_notify+0x35/0x70
> [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70
> [<ffffffff8108304d>] notify_die+0x3d/0x50
> [<ffffffff81017219>] do_int3+0x89/0x120
> [<ffffffff81480fb4>] int3+0x44/0x80
>
> We fix the problem by using irq_work to call schedule_work()
> instead of calling it directly. irq_work is an NMI-safe deferred work
> framework that performs the requested work from a hardirq context
> (usually an IPI but it can be timer interrupt on some
> architectures).
>
> Note that we still need to a workqueue since we cannot resync
> the keyboard state from the hardirq context provided by irq_work.
> That must be done from task context for the calls into the input
> subystem. Hence we must defer the work twice. First to safely
> switch from the debug trap (NMI-like context) to hardirq and
> then, secondly, to get from hardirq to the system workqueue.
>
> Signed-off-by: LiuYe <liu.yeC@h3c.com>
> Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
>
> ---
> V6 -> V7: Add comments in the code.
> V5 -> V6: Replace with a more professional and accurate answer.
> V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
> V3 -> V4: Add changelogs
> V2 -> V3: Add description information
> V1 -> V2: using irq_work to solve this properly.
> ---
> ---
> drivers/tty/serial/kgdboc.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 7ce7bb164..750ed66d2 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -22,6 +22,7 @@
> #include <linux/module.h>
> #include <linux/platform_device.h>
> #include <linux/serial_core.h>
> +#include <linux/irq_work.h>
>
> #define MAX_CONFIG_LEN 40
>
> @@ -98,11 +99,29 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
> }
>
> static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
> +/*
> + * We fix the problem by using irq_work to call schedule_work()
> + * instead of calling it directly.
What problem?
Put another way this text has been copy-pasted from
the commit message without any editing to make it make sense. Text in
the C file needs to be standalone!
More like:
--- cut here ---
This code ensures that the keyboard state, which is changed during kdb
execution, is resynchronized when we leave the debug trap. The resync
logic calls into the input subsystem to force a reset. The calls into
the input subsystem must be executed from normal task context.
We need to trigger the resync from the debug trap, which executes in an
NMI (or similar) context. To make it safe to call into the input
subsystem we end up having use two deferred execution techniques.
Firstly, we use irq_work, which is NMI-safe, to provoke a callback from
hardirq context. Then, from the hardirq callback we use the system
workqueue to provoke the callback that actually performs the resync.
--- cut here ---
> irq_work is an NMI-safe deferred work
> + * framework that performs the requested work from a hardirq context
> + * (usually an IPI but it can be timer interrupt on some
> + * architectures). Note that we still need to a workqueue since we cannot resync
> + * the keyboard state from the hardirq context provided by irq_work.
> + * That must be done from task context for the calls into the input
> + * subystem. Hence we must defer the work twice. First to safely
> + * switch from the debug trap (NMI-like context) to hardirq and
> + * then, secondly, to get from hardirq to the system workqueue.
> + */
Please find a better place to anchor the comment. It should be further
up in the file when the first bit of deferred work appears, perhaps near
kgdboc_restore_input_helper().
> +static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
> +{
> + schedule_work(&kgdboc_restore_input_work);
> +}
> +
> +static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
Daniel.
From: LiuYe <liu.yeC@h3c.com>
Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
attempt to use schedule_work() to provoke a keyboard reset when
transitioning out of the debugger and back to normal operation.
This can cause deadlock because schedule_work() is not NMI-safe.
The stack trace below shows an example of the problem. In this
case the master cpu is not running from NMI but it has parked
the slave CPUs using an NMI and the parked CPUs is holding
spinlocks needed by schedule_work().
example:
BUG: spinlock lockup suspected on CPU#0, namex/10450
lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1
ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000
ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20
Call Trace:
[<ffffffff81479e6d>] ? __schedule+0x16d/0xac0
[<ffffffff8147a7fc>] ? schedule+0x3c/0x90
[<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120
[<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10
[<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0
[<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20
[<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0
[<ffffffff8108c540>] ? wake_up_q+0x70/0x70
[<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0
[<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75
CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1
Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019
0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000
ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980
000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0
Call Trace:
<#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2
[<ffffffff810a7f7f>] spin_dump+0x7f/0x100
[<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150
[<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20
[<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0
[<ffffffff8108c4c5>] wake_up_process+0x15/0x20
[<ffffffff8107b371>] insert_work+0x81/0xc0
[<ffffffff8107b4e5>] __queue_work+0x135/0x390
[<ffffffff8107b786>] queue_work_on+0x46/0x90
[<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70
[<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610
[<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0
[<ffffffff81054e21>] __kgdb_notify+0x71/0xd0
[<ffffffff81054eb5>] kgdb_notify+0x35/0x70
[<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70
[<ffffffff8108304d>] notify_die+0x3d/0x50
[<ffffffff81017219>] do_int3+0x89/0x120
[<ffffffff81480fb4>] int3+0x44/0x80
We fix the problem by using irq_work to call schedule_work()
instead of calling it directly. This is because we cannot
resynchronize the keyboard state from the hardirq context
provided by irq_work. This must be done from the task context
in order to call the input subsystem.
Therefore, we have to defer the work twice. First, safely
switch from the debug trap context (similar to NMI) to the
hardirq, and then switch from the hardirq to the system work queue.
Signed-off-by: LiuYe <liu.yeC@h3c.com>
Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
V7 -> V8: Update the description information and comments in the code.
: Submit this patch based on version linux-6.9-rc2.
V6 -> V7: Add comments in the code.
V5 -> V6: Replace with a more professional and accurate answer.
V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
V3 -> V4: Add changelogs
V2 -> V3: Add description information
V1 -> V2: using irq_work to solve this properly.
---
---
drivers/tty/serial/kgdboc.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164..d6ce945f0 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -22,6 +22,7 @@
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
+#include <linux/irq_work.h>
#define MAX_CONFIG_LEN 40
@@ -82,6 +83,19 @@ static struct input_handler kgdboc_reset_handler = {
static DEFINE_MUTEX(kgdboc_reset_mutex);
+/*
+ * This code ensures that the keyboard state, which is changed during kdb
+ * execution, is resynchronized when we leave the debug trap. The resync
+ * logic calls into the input subsystem to force a reset. The calls into
+ * the input subsystem must be executed from normal task context.
+ *
+ * We need to trigger the resync from the debug trap, which executes in an
+ * NMI (or similar) context. To make it safe to call into the input
+ * subsystem we end up having use two deferred execution techniques.
+ * Firstly, we use irq_work, which is NMI-safe, to provoke a callback from
+ * hardirq context. Then, from the hardirq callback we use the system
+ * workqueue to provoke the callback that actually performs the resync.
+ */
static void kgdboc_restore_input_helper(struct work_struct *dummy)
{
/*
@@ -99,10 +113,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+ schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
static void kgdboc_restore_input(void)
{
if (likely(system_state == SYSTEM_RUNNING))
- schedule_work(&kgdboc_restore_input_work);
+ irq_work_queue(&kgdboc_restore_input_irq_work);
}
static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +154,7 @@ static void kgdboc_unregister_kbd(void)
i--;
}
}
+ irq_work_sync(&kgdboc_restore_input_irq_work);
flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
--
2.25.1Wed, Apr 03, 2024 at 02:11:09PM +0800, liu.yec@h3c.com kirjoitti: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > The stack trace below shows an example of the problem. In this > case the master cpu is not running from NMI but it has parked > the slave CPUs using an NMI and the parked CPUs is holding > spinlocks needed by schedule_work(). > example: > BUG: spinlock lockup suspected on CPU#0, namex/10450 > lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1 > ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000 > ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20 > Call Trace: > [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0 > [<ffffffff8147a7fc>] ? schedule+0x3c/0x90 > [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120 > [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10 > [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0 > [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20 > [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0 > [<ffffffff8108c540>] ? wake_up_q+0x70/0x70 > [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0 > [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75 > CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1 > Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019 > 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000 > ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980 > 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0 > Call Trace: > <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2 > [<ffffffff810a7f7f>] spin_dump+0x7f/0x100 > [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150 > [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20 > [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0 > [<ffffffff8108c4c5>] wake_up_process+0x15/0x20 > [<ffffffff8107b371>] insert_work+0x81/0xc0 > [<ffffffff8107b4e5>] __queue_work+0x135/0x390 > [<ffffffff8107b786>] queue_work_on+0x46/0x90 > [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70 > [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610 > [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0 > [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0 > [<ffffffff81054eb5>] kgdb_notify+0x35/0x70 > [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70 > [<ffffffff8108304d>] notify_die+0x3d/0x50 > [<ffffffff81017219>] do_int3+0x89/0x120 > [<ffffffff81480fb4>] int3+0x44/0x80 Ouch. Please, read this https://www.kernel.org/doc/html/latest/process/submitting-patches.html#backtraces-in-commit-messages and modify the commit message accordingly. > We fix the problem by using irq_work to call schedule_work() > instead of calling it directly. This is because we cannot > resynchronize the keyboard state from the hardirq context > provided by irq_work. This must be done from the task context > in order to call the input subsystem. > > Therefore, we have to defer the work twice. First, safely > switch from the debug trap context (similar to NMI) to the > hardirq, and then switch from the hardirq to the system work queue. > Signed-off-by: LiuYe <liu.yeC@h3c.com> > Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> Correct tag is Co-developed-by, btw it's written in the same document the link to which I provided a few lines above. ... > --- a/drivers/tty/serial/kgdboc.c > +++ b/drivers/tty/serial/kgdboc.c > @@ -22,6 +22,7 @@ > #include <linux/module.h> > #include <linux/platform_device.h> > #include <linux/serial_core.h> > +#include <linux/irq_work.h> Please, keep it ordered (with visible context this should go at least before module.h). -- With Best Regards, Andy Shevchenko
>Wed, Apr 03, 2024 at 02:11:09PM +0800, liu.yec@h3c.com kirjoitti: >> From: LiuYe <liu.yeC@h3c.com> >> >> Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will >> attempt to use schedule_work() to provoke a keyboard reset when >> transitioning out of the debugger and back to normal operation. >> This can cause deadlock because schedule_work() is not NMI-safe. >> >> The stack trace below shows an example of the problem. In this >> case the master cpu is not running from NMI but it has parked >> the slave CPUs using an NMI and the parked CPUs is holding >> spinlocks needed by schedule_work(). > >> example: >> BUG: spinlock lockup suspected on CPU#0, namex/10450 >> lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1 >> ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000 >> ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20 >> Call Trace: >> [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0 >> [<ffffffff8147a7fc>] ? schedule+0x3c/0x90 >> [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120 >> [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10 >> [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0 >> [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20 >> [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0 >> [<ffffffff8108c540>] ? wake_up_q+0x70/0x70 >> [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0 >> [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75 >> CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1 >> Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019 >> 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000 >> ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980 >> 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0 >> Call Trace: >> <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2 >> [<ffffffff810a7f7f>] spin_dump+0x7f/0x100 >> [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150 >> [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20 >> [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0 >> [<ffffffff8108c4c5>] wake_up_process+0x15/0x20 >> [<ffffffff8107b371>] insert_work+0x81/0xc0 >> [<ffffffff8107b4e5>] __queue_work+0x135/0x390 >> [<ffffffff8107b786>] queue_work_on+0x46/0x90 >> [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70 >> [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610 >> [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0 >> [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0 >> [<ffffffff81054eb5>] kgdb_notify+0x35/0x70 >> [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70 >> [<ffffffff8108304d>] notify_die+0x3d/0x50 >> [<ffffffff81017219>] do_int3+0x89/0x120 >> [<ffffffff81480fb4>] int3+0x44/0x80 > >Ouch. >Please, read this >https://www.kernel.org/doc/html/latest/process/submitting-patches.html#backtraces-in-commit-messages >and modify the commit message accordingly. The example is the printout of the kernel lockup detection mechanism, which may be easier to understand. If organized according to the format provided in the previous link, should it be arranged as follows? Example: BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1 CPU1: Call Trace: __schedule schedule schedule_hrtimeout_range_clock mutex_unlock ep_scan_ready_list schedule_hrtimeout_range ep_poll wake_up_q SyS_epoll_wait entry_SYSCALL_64_fastpath CPU0: Call Trace: dump_stack spin_dump do_raw_spin_lock _raw_spin_lock try_to_wake_up wake_up_process insert_work __queue_work queue_work_on kgdboc_post_exp_handler kgdb_cpu_enter kgdb_handle_exception __kgdb_notify kgdb_notify notifier_call_chain notify_die do_int3 int3 >> We fix the problem by using irq_work to call schedule_work() >> instead of calling it directly. This is because we cannot >> resynchronize the keyboard state from the hardirq context >> provided by irq_work. This must be done from the task context >> in order to call the input subsystem. >> >> Therefore, we have to defer the work twice. First, safely >> switch from the debug trap context (similar to NMI) to the >> hardirq, and then switch from the hardirq to the system work queue. > >> Signed-off-by: LiuYe <liu.yeC@h3c.com> >> Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> > >Correct tag is Co-developed-by, btw it's written in the same document the link >to which I provided a few lines above. Yes, there will be warnings when using the ./scripts/checkpatch.pl script to check. WARNING: Non-standard signature: Co-authored-by: #68: Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> total: 0 errors, 1 warnings, 51 lines checked I will change it to the following: Co-developed-by: Daniel Thompson <daniel.thompson@linaro.org> > >> --- a/drivers/tty/serial/kgdboc.c >> +++ b/drivers/tty/serial/kgdboc.c >> @@ -22,6 +22,7 @@ >> #include <linux/module.h> >> #include <linux/platform_device.h> >> #include <linux/serial_core.h> >> +#include <linux/irq_work.h> > >Please, keep it ordered (with visible context this should go at least before >module.h). I don't understand why this needs to be placed before module.h. Please explain further, thank you.
On Mon, Apr 8, 2024 at 4:46 AM LiuYe <liu.yeC@h3c.com> wrote: > >Wed, Apr 03, 2024 at 02:11:09PM +0800, liu.yec@h3c.com kirjoitti: ... > >Ouch. > >Please, read this > >https://www.kernel.org/doc/html/latest/process/submitting-patches.html#backtraces-in-commit-messages > >and modify the commit message accordingly. > > The example is the printout of the kernel lockup detection mechanism, which may be easier to understand. > If organized according to the format provided in the previous link, should it be arranged as follows? Do you think all lines are important from this? Do you think you haven't dropped anything useful? If "yes" is the answer to both Qs, then go with it (but at least I see that first seems to me as "no", some lines are not important) > Example: > BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1 > CPU1: Call Trace: > __schedule > schedule > schedule_hrtimeout_range_clock > mutex_unlock > ep_scan_ready_list > schedule_hrtimeout_range > ep_poll > wake_up_q > SyS_epoll_wait > entry_SYSCALL_64_fastpath > > CPU0: Call Trace: > dump_stack > spin_dump > do_raw_spin_lock > _raw_spin_lock > try_to_wake_up > wake_up_process > insert_work > __queue_work > queue_work_on > kgdboc_post_exp_handler > kgdb_cpu_enter > kgdb_handle_exception > __kgdb_notify > kgdb_notify > notifier_call_chain > notify_die > do_int3 > int3 ... > >> #include <linux/module.h> > >> #include <linux/platform_device.h> > >> #include <linux/serial_core.h> > >> +#include <linux/irq_work.h> > > > >Please, keep it ordered (with visible context this should go at least before > >module.h). > > I don't understand why this needs to be placed before module.h. Please explain further, thank you. Alphabetical order helps long-term maintenance. Yes, I know that it is not _fully_ sorted, but don't add more mess to it. -- With Best Regards, Andy Shevchenko
From: LiuYe <liu.yeC@h3c.com>
Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
attempt to use schedule_work() to provoke a keyboard reset when
transitioning out of the debugger and back to normal operation.
This can cause deadlock because schedule_work() is not NMI-safe.
The stack trace below shows an example of the problem. In this
case the master cpu is not running from NMI but it has parked
the slave CPUs using an NMI and the parked CPUs is holding
spinlocks needed by schedule_work().
Example:
BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1
CPU1: Call Trace:
__schedule
schedule
schedule_hrtimeout_range_clock
mutex_unlock
ep_scan_ready_list
schedule_hrtimeout_range
ep_poll
wake_up_q
SyS_epoll_wait
entry_SYSCALL_64_fastpath
CPU0: Call Trace:
dump_stack
spin_dump
do_raw_spin_lock
_raw_spin_lock
try_to_wake_up
wake_up_process
insert_work
__queue_work
queue_work_on
kgdboc_post_exp_handler
kgdb_cpu_enter
kgdb_handle_exception
__kgdb_notify
kgdb_notify
notifier_call_chain
notify_die
do_int3
int3
We fix the problem by using irq_work to call schedule_work()
instead of calling it directly. This is because we cannot
resynchronize the keyboard state from the hardirq context
provided by irq_work. This must be done from the task context
in order to call the input subsystem.
Therefore, we have to defer the work twice. First, safely
switch from the debug trap context (similar to NMI) to the
hardirq, and then switch from the hardirq to the system work queue.
Signed-off-by: LiuYe <liu.yeC@h3c.com>
Co-developed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
V8 -> V9: Modify call trace format and move irq_work.h before module.h
V7 -> V8: Update the description information and comments in the code.
: Submit this patch based on version linux-6.9-rc2.
V6 -> V7: Add comments in the code.
V5 -> V6: Replace with a more professional and accurate answer.
V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
V3 -> V4: Add changelogs
V2 -> V3: Add description information
V1 -> V2: using irq_work to solve this properly.
---
---
drivers/tty/serial/kgdboc.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164..32410fec7 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -19,6 +19,7 @@
#include <linux/console.h>
#include <linux/vt_kern.h>
#include <linux/input.h>
+#include <linux/irq_work.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
@@ -82,6 +83,19 @@ static struct input_handler kgdboc_reset_handler = {
static DEFINE_MUTEX(kgdboc_reset_mutex);
+/*
+ * This code ensures that the keyboard state, which is changed during kdb
+ * execution, is resynchronized when we leave the debug trap. The resync
+ * logic calls into the input subsystem to force a reset. The calls into
+ * the input subsystem must be executed from normal task context.
+ *
+ * We need to trigger the resync from the debug trap, which executes in an
+ * NMI (or similar) context. To make it safe to call into the input
+ * subsystem we end up having use two deferred execution techniques.
+ * Firstly, we use irq_work, which is NMI-safe, to provoke a callback from
+ * hardirq context. Then, from the hardirq callback we use the system
+ * workqueue to provoke the callback that actually performs the resync.
+ */
static void kgdboc_restore_input_helper(struct work_struct *dummy)
{
/*
@@ -99,10 +113,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+ schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
static void kgdboc_restore_input(void)
{
if (likely(system_state == SYSTEM_RUNNING))
- schedule_work(&kgdboc_restore_input_work);
+ irq_work_queue(&kgdboc_restore_input_irq_work);
}
static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +154,7 @@ static void kgdboc_unregister_kbd(void)
i--;
}
}
+ irq_work_sync(&kgdboc_restore_input_irq_work);
flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
--
2.25.1From: LiuYe <liu.yeC@h3c.com>
Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
attempt to use schedule_work() to provoke a keyboard reset when
transitioning out of the debugger and back to normal operation.
This can cause deadlock because schedule_work() is not NMI-safe.
The stack trace below shows an example of the problem. In this
case the master cpu is not running from NMI but it has parked
the slave CPUs using an NMI and the parked CPUs is holding
spinlocks needed by schedule_work().
Example:
BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1
CPU1: Call Trace:
__schedule
schedule
schedule_hrtimeout_range_clock
mutex_unlock
ep_scan_ready_list
schedule_hrtimeout_range
ep_poll
wake_up_q
SyS_epoll_wait
entry_SYSCALL_64_fastpath
CPU0: Call Trace:
dump_stack
spin_dump
do_raw_spin_lock
_raw_spin_lock
try_to_wake_up
wake_up_process
insert_work
__queue_work
queue_work_on
kgdboc_post_exp_handler
kgdb_cpu_enter
kgdb_handle_exception
__kgdb_notify
kgdb_notify
notifier_call_chain
notify_die
do_int3
int3
We fix the problem by using irq_work to call schedule_work()
instead of calling it directly. This is because we cannot
resynchronize the keyboard state from the hardirq context
provided by irq_work. This must be done from the task context
in order to call the input subsystem.
Therefore, we have to defer the work twice. First, safely
switch from the debug trap context (similar to NMI) to the
hardirq, and then switch from the hardirq to the system work queue.
Signed-off-by: LiuYe <liu.yeC@h3c.com>
Co-developed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Greg KH <gregkh@linuxfoundation.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
---
V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, Acked-by of Daniel Thompson
V8 -> V9: Modify call trace format and move irq_work.h before module.h
V7 -> V8: Update the description information and comments in the code.
: Submit this patch based on version linux-6.9-rc2.
V6 -> V7: Add comments in the code.
V5 -> V6: Replace with a more professional and accurate answer.
V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
V3 -> V4: Add changelogs
V2 -> V3: Add description information
V1 -> V2: using irq_work to solve this properly.
---
---
drivers/tty/serial/kgdboc.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164..32410fec7 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -19,6 +19,7 @@
#include <linux/console.h>
#include <linux/vt_kern.h>
#include <linux/input.h>
+#include <linux/irq_work.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
@@ -82,6 +83,19 @@ static struct input_handler kgdboc_reset_handler = {
static DEFINE_MUTEX(kgdboc_reset_mutex);
+/*
+ * This code ensures that the keyboard state, which is changed during kdb
+ * execution, is resynchronized when we leave the debug trap. The resync
+ * logic calls into the input subsystem to force a reset. The calls into
+ * the input subsystem must be executed from normal task context.
+ *
+ * We need to trigger the resync from the debug trap, which executes in an
+ * NMI (or similar) context. To make it safe to call into the input
+ * subsystem we end up having use two deferred execution techniques.
+ * Firstly, we use irq_work, which is NMI-safe, to provoke a callback from
+ * hardirq context. Then, from the hardirq callback we use the system
+ * workqueue to provoke the callback that actually performs the resync.
+ */
static void kgdboc_restore_input_helper(struct work_struct *dummy)
{
/*
@@ -99,10 +113,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+ schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
static void kgdboc_restore_input(void)
{
if (likely(system_state == SYSTEM_RUNNING))
- schedule_work(&kgdboc_restore_input_work);
+ irq_work_queue(&kgdboc_restore_input_irq_work);
}
static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +154,7 @@ static void kgdboc_unregister_kbd(void)
i--;
}
}
+ irq_work_sync(&kgdboc_restore_input_irq_work);
flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
--
2.25.1On Wed, Apr 10, 2024 at 10:06:15AM +0800, liu.yec@h3c.com wrote: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > The stack trace below shows an example of the problem. In this > case the master cpu is not running from NMI but it has parked > the slave CPUs using an NMI and the parked CPUs is holding > spinlocks needed by schedule_work(). > > Example: > BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1 > CPU1: Call Trace: > __schedule > schedule > schedule_hrtimeout_range_clock > mutex_unlock > ep_scan_ready_list > schedule_hrtimeout_range > ep_poll > wake_up_q > SyS_epoll_wait > entry_SYSCALL_64_fastpath > > CPU0: Call Trace: > dump_stack > spin_dump > do_raw_spin_lock > _raw_spin_lock > try_to_wake_up > wake_up_process > insert_work > __queue_work > queue_work_on > kgdboc_post_exp_handler > kgdb_cpu_enter > kgdb_handle_exception > __kgdb_notify > kgdb_notify > notifier_call_chain > notify_die > do_int3 > int3 > > We fix the problem by using irq_work to call schedule_work() > instead of calling it directly. This is because we cannot > resynchronize the keyboard state from the hardirq context > provided by irq_work. This must be done from the task context > in order to call the input subsystem. > > Therefore, we have to defer the work twice. First, safely > switch from the debug trap context (similar to NMI) to the > hardirq, and then switch from the hardirq to the system work queue. > > Signed-off-by: LiuYe <liu.yeC@h3c.com> > Co-developed-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Greg KH <gregkh@linuxfoundation.org> I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. greg k-h
>> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> > >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? > >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. > >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> > >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, Acked-by >> of Daniel Thompson > >Huh?! @greg k-h ： @Andy Shevchenko ： Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. I want to express my gratitude for the suggestions on the patch from the two of you. What do I need to do now? Release PATCH V11 and delete these two signatures in it ?
On Wed, Apr 10, 2024 at 05:54:08AM +0000, Liuye wrote: > >> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> > > > >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? > > > >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. > > > > >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> > > > >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, Acked-by > >> of Daniel Thompson > > > >Huh?! > > @greg k-h ： > @Andy Shevchenko ： > > Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. > > I want to express my gratitude for the suggestions on the patch from the two of you. > > What do I need to do now? Release PATCH V11 and delete these two signatures in it ? As I said, go work with your corporate lawyers on this to understand what just happened and have them let us know how it will not happen again. thanks, greg k-h
>On Wed, Apr 10, 2024 at 05:54:08AM +0000, Liuye wrote: >> >> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> >> > >> >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? >> > >> >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. >> > >> >> >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> >> > >> >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, >> >> Acked-by of Daniel Thompson >> > >> >Huh?! >> >> @greg k-h ： >> @Andy Shevchenko ： >> >> Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. >> >> I want to express my gratitude for the suggestions on the patch from the two of you. >> >> What do I need to do now? Release PATCH V11 and delete these two signatures in it ? > >As I said, go work with your corporate lawyers on this to understand what just happened and have them let us know how it will not happen again. I'm very sorry, this is my first time submitting a patch and I made a significant mistake in using "Signed-off-by". I now understand the meaning of this field and will not make the same mistake again in the future. Thanks， Liu Ye
On Wed, Apr 10, 2024 at 06:10:10AM +0000, Liuye wrote: > >On Wed, Apr 10, 2024 at 05:54:08AM +0000, Liuye wrote: > >> >> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> > >> > > >> >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? > >> > > >> >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. > >> > > >> > >> >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> > >> > > >> >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, > >> >> Acked-by of Daniel Thompson > >> > > >> >Huh?! > >> > >> @greg k-h ： > >> @Andy Shevchenko ： > >> > >> Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. > >> > >> I want to express my gratitude for the suggestions on the patch from the two of you. > >> > >> What do I need to do now? Release PATCH V11 and delete these two signatures in it ? > > > >As I said, go work with your corporate lawyers on this to understand what just happened and have them let us know how it will not happen again. > > I'm very sorry, this is my first time submitting a patch and I made a significant mistake in using "Signed-off-by". I now understand the meaning of this field and will not make the same mistake again in the future. Understood, but you still need to go work with your corporate legal group so that you all ensure this does not happen again for any other developer in your company, as I am sure they will want to know about this. thanks, greg k-h
>On Wed, Apr 10, 2024 at 06:10:10AM +0000, Liuye wrote: >> >On Wed, Apr 10, 2024 at 05:54:08AM +0000, Liuye wrote: >> >> >> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> >> >> > >> >> >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? >> >> > >> >> >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. >> >> > >> >> >> >> >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> >> >> > >> >> >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, >> >> >> Acked-by of Daniel Thompson >> >> > >> >> >Huh?! >> >> >> >> @greg k-h ： >> >> @Andy Shevchenko ： >> >> >> >> Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. >> >> >> >> I want to express my gratitude for the suggestions on the patch from the two of you. >> >> >> >> What do I need to do now? Release PATCH V11 and delete these two signatures in it ? >> > >> >As I said, go work with your corporate lawyers on this to understand what just happened and have them let us know how it will not happen again. >> >> I'm very sorry, this is my first time submitting a patch and I made a significant mistake in using "Signed-off-by". I now understand the meaning of this field and will not make the same mistake again in the future. > >Understood, but you still need to go work with your corporate legal group so that you all ensure this does not happen again for any other developer in your company, as I am sure they will want to know about this. Ok, I will report this to the company. At the same time, I will add an audit mechanism to the patch submission process. Thanks again for your reminder. I will remove this part in PATCH V11. Thanks， Liu Ye
On Wed, Apr 10, 2024 at 06:30:59AM +0000, Liuye wrote: > >On Wed, Apr 10, 2024 at 06:10:10AM +0000, Liuye wrote: > >> >On Wed, Apr 10, 2024 at 05:54:08AM +0000, Liuye wrote: > >> >> >> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> > >> >> > > >> >> >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? > >> >> > > >> >> >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. > >> >> > > >> >> > >> >> >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> > >> >> > > >> >> >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, > >> >> >> Acked-by of Daniel Thompson > >> >> > > >> >> >Huh?! > >> >> > >> >> @greg k-h ： > >> >> @Andy Shevchenko ： > >> >> > >> >> Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. > >> >> > >> >> I want to express my gratitude for the suggestions on the patch from the two of you. > >> >> > >> >> What do I need to do now? Release PATCH V11 and delete these two signatures in it ? > >> > > >> >As I said, go work with your corporate lawyers on this to understand what just happened and have them let us know how it will not happen again. > >> > >> I'm very sorry, this is my first time submitting a patch and I made a significant mistake in using "Signed-off-by". I now understand the meaning of this field and will not make the same mistake again in the future. > > > >Understood, but you still need to go work with your corporate legal group so that you all ensure this does not happen again for any other developer in your company, as I am sure they will want to know about this. > > Ok, I will report this to the company. At the same time, I will add an audit mechanism to the patch submission process. Thanks again for your reminder. > > I will remove this part in PATCH V11. No, you will need to do this before we can accept your change. And some sort of verification that this is now in place properly for obvious reasons. thanks, greg k-h
>On Wed, Apr 10, 2024 at 06:30:59AM +0000, Liuye wrote: >> >On Wed, Apr 10, 2024 at 06:10:10AM +0000, Liuye wrote: >> >> >On Wed, Apr 10, 2024 at 05:54:08AM +0000, Liuye wrote: >> >> >> >> Signed-off-by: Greg KH <gregkh@linuxfoundation.org> >> >> >> > >> >> >> >I have NOT signed off on this commit. You just said that I made a legal statement about this commit without that actually being true??? >> >> >> > >> >> >> >Sorry, but that is flat out not acceptable at all. Please go work with your company lawyers to figure out what you did and come back with an explaination of exactly what this is and how it will not happen again. >> >> >> > >> >> >> >> >> >> >> Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> >> >> >> > >> >> >> >> V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, >> >> >> >> Acked-by of Daniel Thompson >> >> >> > >> >> >> >Huh?! >> >> >> >> >> >> @greg k-h ： >> >> >> @Andy Shevchenko ： >> >> >> >> >> >> Sorry, it was my mistake. I misunderstood the meaning of "signed-off-by", which led to usage issues. >> >> >> >> >> >> I want to express my gratitude for the suggestions on the patch from the two of you. >> >> >> >> >> >> What do I need to do now? Release PATCH V11 and delete these two signatures in it ? >> >> > >> >> >As I said, go work with your corporate lawyers on this to understand what just happened and have them let us know how it will not happen again. >> >> >> >> I'm very sorry, this is my first time submitting a patch and I made a significant mistake in using "Signed-off-by". I now understand the meaning of this field and will not make the same mistake again in the future. >> > >> >Understood, but you still need to go work with your corporate legal group so that you all ensure this does not happen again for any other developer in your company, as I am sure they will want to know about this. >> >> Ok, I will report this to the company. At the same time, I will add an audit mechanism to the patch submission process. Thanks again for your reminder. >> >> I will remove this part in PATCH V11. > >No, you will need to do this before we can accept your change. And some sort of verification that this is now in place properly for obvious reasons. What does "No" mean? Are you talking about giving feedback to the company to prevent this incident from happening? Or submitting PATCH V11? If it's the former, how should I give you feedback?"
From: LiuYe <liu.yeC@h3c.com>
Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
attempt to use schedule_work() to provoke a keyboard reset when
transitioning out of the debugger and back to normal operation.
This can cause deadlock because schedule_work() is not NMI-safe.
The stack trace below shows an example of the problem. In this
case the master cpu is not running from NMI but it has parked
the slave CPUs using an NMI and the parked CPUs is holding
spinlocks needed by schedule_work().
Example:
BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1
CPU1: Call Trace:
__schedule
schedule
schedule_hrtimeout_range_clock
mutex_unlock
ep_scan_ready_list
schedule_hrtimeout_range
ep_poll
wake_up_q
SyS_epoll_wait
entry_SYSCALL_64_fastpath
CPU0: Call Trace:
dump_stack
spin_dump
do_raw_spin_lock
_raw_spin_lock
try_to_wake_up
wake_up_process
insert_work
__queue_work
queue_work_on
kgdboc_post_exp_handler
kgdb_cpu_enter
kgdb_handle_exception
__kgdb_notify
kgdb_notify
notifier_call_chain
notify_die
do_int3
int3
We fix the problem by using irq_work to call schedule_work()
instead of calling it directly. This is because we cannot
resynchronize the keyboard state from the hardirq context
provided by irq_work. This must be done from the task context
in order to call the input subsystem.
Therefore, we have to defer the work twice. First, safely
switch from the debug trap context (similar to NMI) to the
hardirq, and then switch from the hardirq to the system work queue.
Signed-off-by: LiuYe <liu.yeC@h3c.com>
Co-developed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
---
V10 -> V11: Revert to V9
V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, Acked-by of Daniel Thompson
V8 -> V9: Modify call trace format and move irq_work.h before module.h
V7 -> V8: Update the description information and comments in the code.
: Submit this patch based on version linux-6.9-rc2.
V6 -> V7: Add comments in the code.
V5 -> V6: Replace with a more professional and accurate answer.
V4 -> V5: Answer why schedule another work in the irq_work and not do the job directly.
V3 -> V4: Add changelogs
V2 -> V3: Add description information
V1 -> V2: using irq_work to solve this properly.
---
---
drivers/tty/serial/kgdboc.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 7ce7bb164..32410fec7 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -19,6 +19,7 @@
#include <linux/console.h>
#include <linux/vt_kern.h>
#include <linux/input.h>
+#include <linux/irq_work.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>
@@ -82,6 +83,19 @@ static struct input_handler kgdboc_reset_handler = {
static DEFINE_MUTEX(kgdboc_reset_mutex);
+/*
+ * This code ensures that the keyboard state, which is changed during kdb
+ * execution, is resynchronized when we leave the debug trap. The resync
+ * logic calls into the input subsystem to force a reset. The calls into
+ * the input subsystem must be executed from normal task context.
+ *
+ * We need to trigger the resync from the debug trap, which executes in an
+ * NMI (or similar) context. To make it safe to call into the input
+ * subsystem we end up having use two deferred execution techniques.
+ * Firstly, we use irq_work, which is NMI-safe, to provoke a callback from
+ * hardirq context. Then, from the hardirq callback we use the system
+ * workqueue to provoke the callback that actually performs the resync.
+ */
static void kgdboc_restore_input_helper(struct work_struct *dummy)
{
/*
@@ -99,10 +113,17 @@ static void kgdboc_restore_input_helper(struct work_struct *dummy)
static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);
+static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
+{
+ schedule_work(&kgdboc_restore_input_work);
+}
+
+static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);
+
static void kgdboc_restore_input(void)
{
if (likely(system_state == SYSTEM_RUNNING))
- schedule_work(&kgdboc_restore_input_work);
+ irq_work_queue(&kgdboc_restore_input_irq_work);
}
static int kgdboc_register_kbd(char **cptr)
@@ -133,6 +154,7 @@ static void kgdboc_unregister_kbd(void)
i--;
}
}
+ irq_work_sync(&kgdboc_restore_input_irq_work);
flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
--
2.25.1On Wed, Apr 10, 2024 at 5:07 AM <liu.yec@h3c.com> wrote: > > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > The stack trace below shows an example of the problem. In this > case the master cpu is not running from NMI but it has parked > the slave CPUs using an NMI and the parked CPUs is holding > spinlocks needed by schedule_work(). > > Example: > BUG: spinlock lockup suspected on CPU#0. owner_cpu: 1 > CPU1: Call Trace: > __schedule > schedule > schedule_hrtimeout_range_clock > mutex_unlock > ep_scan_ready_list > schedule_hrtimeout_range > ep_poll > wake_up_q > SyS_epoll_wait > entry_SYSCALL_64_fastpath > > CPU0: Call Trace: > dump_stack > spin_dump > do_raw_spin_lock > _raw_spin_lock > try_to_wake_up > wake_up_process > insert_work > __queue_work > queue_work_on > kgdboc_post_exp_handler > kgdb_cpu_enter > kgdb_handle_exception > __kgdb_notify > kgdb_notify > notifier_call_chain > notify_die > do_int3 > int3 > > We fix the problem by using irq_work to call schedule_work() > instead of calling it directly. This is because we cannot > resynchronize the keyboard state from the hardirq context > provided by irq_work. This must be done from the task context > in order to call the input subsystem. > > Therefore, we have to defer the work twice. First, safely > switch from the debug trap context (similar to NMI) to the > hardirq, and then switch from the hardirq to the system work queue. ... > Signed-off-by: Greg KH <gregkh@linuxfoundation.org> > Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com> > V9 -> V10 : Add Signed-off-by of Greg KH and Andy Shevchenko, Acked-by of Daniel Thompson Huh?! -- With Best Regards, Andy Shevchenko
On Wed, Apr 03, 2024 at 02:11:09PM +0800, liu.yec@h3c.com wrote: > From: LiuYe <liu.yeC@h3c.com> > > Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will > attempt to use schedule_work() to provoke a keyboard reset when > transitioning out of the debugger and back to normal operation. > This can cause deadlock because schedule_work() is not NMI-safe. > > <snip> > > We fix the problem by using irq_work to call schedule_work() > instead of calling it directly. This is because we cannot > resynchronize the keyboard state from the hardirq context > provided by irq_work. This must be done from the task context > in order to call the input subsystem. > > Therefore, we have to defer the work twice. First, safely > switch from the debug trap context (similar to NMI) to the > hardirq, and then switch from the hardirq to the system work queue. > > Signed-off-by: LiuYe <liu.yeC@h3c.com> > Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org> > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> I'm happy with how this is looking. In the long term it might be good to move the keyboard resync code so it is with the rest of the kdb keyboard code rather than in tty/serial. However I certainly don't want to tangle that kind of clean up along with a bug fix so I think this is ready to go now. @Greg: I assume you want to take this via the tty/serial tree? I contributed a fair bit to the eventual patch so a Reviewed-by from me probably isn't appropriate but if you want to take the code it is certainly: Acked-by: Daniel Thompson <daniel.thompson@linaro.org> Daniel.
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