1. Patchew
  2. linux
  3. [PATCH v5 0/6] perf: Make SIGTRAP and __perf_pending_irq() work on RT.
  4. View patch

[PATCH v5 2/7] task_work: Add TWA_NMI_CURRENT as an additional notify mode.

Sebastian Andrzej Siewior posted 6 patches 1 year, 5 months ago
[PATCH v5 2/7] task_work: Add TWA_NMI_CURRENT as an additional notify mode.
Posted by Sebastian Andrzej Siewior 1 year, 5 months ago 
Adding task_work from NMI context requires the following:
- The kasan_record_aux_stack() is not NMU safe and must be avoided.
- Using TWA_RESUME is NMI safe. If the NMI occurs while the CPU is in
  userland then it will continue in userland and not invoke the `work'
  callback.

Add TWA_NMI_CURRENT as an additional notify mode. In this mode skip
kasan and use irq_work in hardirq-mode to for needed interrupt. Set
TIF_NOTIFY_RESUME within the irq_work callback due to k[ac]san
instrumentation in test_and_set_bit() which does not look NMI safe in
case of a report.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/task_work.h |  1 +
 kernel/task_work.c        | 25 ++++++++++++++++++++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index 26b8a47f41fca..cf5e7e891a776 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -18,6 +18,7 @@ enum task_work_notify_mode {
 	TWA_RESUME,
 	TWA_SIGNAL,
 	TWA_SIGNAL_NO_IPI,
+	TWA_NMI_CURRENT,
 };
 
 static inline bool task_work_pending(struct task_struct *task)
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 2134ac8057a94..05fb41fe09f5d 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -1,10 +1,19 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/irq_work.h>
 #include <linux/spinlock.h>
 #include <linux/task_work.h>
 #include <linux/resume_user_mode.h>
+#include <trace/events/ipi.h>
 
 static struct callback_head work_exited; /* all we need is ->next == NULL */
 
+static void task_work_set_notify_irq(struct irq_work *entry)
+{
+	test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+}
+static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
+	IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
+
 /**
  * task_work_add - ask the @task to execute @work->func()
  * @task: the task which should run the callback
@@ -12,7 +21,7 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */
  * @notify: how to notify the targeted task
  *
  * Queue @work for task_work_run() below and notify the @task if @notify
- * is @TWA_RESUME, @TWA_SIGNAL, or @TWA_SIGNAL_NO_IPI.
+ * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.
  *
  * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
  * task and run the task_work, regardless of whether the task is currently
@@ -24,6 +33,8 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */
  * kernel anyway.
  * @TWA_RESUME work is run only when the task exits the kernel and returns to
  * user mode, or before entering guest mode.
+ * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the
+ * current @task and if the current context is NMI.
  *
  * Fails if the @task is exiting/exited and thus it can't process this @work.
  * Otherwise @work->func() will be called when the @task goes through one of
@@ -44,8 +55,13 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 {
 	struct callback_head *head;
 
-	/* record the work call stack in order to print it in KASAN reports */
-	kasan_record_aux_stack(work);
+	if (notify == TWA_NMI_CURRENT) {
+		if (WARN_ON_ONCE(task != current))
+			return -EINVAL;
+	} else {
+		/* record the work call stack in order to print it in KASAN reports */
+		kasan_record_aux_stack(work);
+	}
 
 	head = READ_ONCE(task->task_works);
 	do {
@@ -66,6 +82,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 	case TWA_SIGNAL_NO_IPI:
 		__set_notify_signal(task);
 		break;
+	case TWA_NMI_CURRENT:
+		irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
+		break;
 	default:
 		WARN_ON_ONCE(1);
 		break;
-- 
2.45.2
Re: [PATCH v5 2/7] task_work: Add TWA_NMI_CURRENT as an additional notify mode.
Posted by Sebastian Andrzej Siewior 1 year, 5 months ago 
On 2024-07-04 19:03:36 [+0200], To linux-perf-users@vger.kernel.org wrote:
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 2134ac8057a94..05fb41fe09f5d 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -1,10 +1,19 @@
>  // SPDX-License-Identifier: GPL-2.0
> +#include <linux/irq_work.h>
>  #include <linux/spinlock.h>
>  #include <linux/task_work.h>
>  #include <linux/resume_user_mode.h>
> +#include <trace/events/ipi.h>

Just noticed that this trace include does not belong here. It is a
leftover from an earlier iteration where I intended to use
smp_send_reschedule() instead of irq_work…

Should I repost the series, or just this one?

Sebastian
Re: [PATCH v5 2/7] task_work: Add TWA_NMI_CURRENT as an additional notify mode.
Posted by Peter Zijlstra 1 year, 5 months ago 
On Fri, Jul 05, 2024 at 04:00:20PM +0200, Sebastian Andrzej Siewior wrote:
> On 2024-07-04 19:03:36 [+0200], To linux-perf-users@vger.kernel.org wrote:
> > diff --git a/kernel/task_work.c b/kernel/task_work.c
> > index 2134ac8057a94..05fb41fe09f5d 100644
> > --- a/kernel/task_work.c
> > +++ b/kernel/task_work.c
> > @@ -1,10 +1,19 @@
> >  // SPDX-License-Identifier: GPL-2.0
> > +#include <linux/irq_work.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/task_work.h>
> >  #include <linux/resume_user_mode.h>
> > +#include <trace/events/ipi.h>
> 
> Just noticed that this trace include does not belong here. It is a
> leftover from an earlier iteration where I intended to use
> smp_send_reschedule() instead of irq_work…
> 
> Should I repost the series, or just this one?

I'll zap it. no worries.
[tip: perf/core] task_work: Add TWA_NMI_CURRENT as an additional notify mode.
Posted by tip-bot2 for Sebastian Andrzej Siewior 1 year, 5 months ago 
The following commit has been merged into the perf/core branch of tip:

Commit-ID:     466e4d801cd438a1ab2c8a2cce1bef6b65c31bbb
Gitweb:        https://git.kernel.org/tip/466e4d801cd438a1ab2c8a2cce1bef6b65c31bbb
Author:        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
AuthorDate:    Thu, 04 Jul 2024 19:03:36 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 09 Jul 2024 13:26:34 +02:00

task_work: Add TWA_NMI_CURRENT as an additional notify mode.

Adding task_work from NMI context requires the following:
- The kasan_record_aux_stack() is not NMU safe and must be avoided.
- Using TWA_RESUME is NMI safe. If the NMI occurs while the CPU is in
  userland then it will continue in userland and not invoke the `work'
  callback.

Add TWA_NMI_CURRENT as an additional notify mode. In this mode skip
kasan and use irq_work in hardirq-mode to for needed interrupt. Set
TIF_NOTIFY_RESUME within the irq_work callback due to k[ac]san
instrumentation in test_and_set_bit() which does not look NMI safe in
case of a report.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240704170424.1466941-3-bigeasy@linutronix.de
---
 include/linux/task_work.h |  1 +
 kernel/task_work.c        | 24 +++++++++++++++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index 26b8a47..cf5e7e8 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -18,6 +18,7 @@ enum task_work_notify_mode {
 	TWA_RESUME,
 	TWA_SIGNAL,
 	TWA_SIGNAL_NO_IPI,
+	TWA_NMI_CURRENT,
 };
 
 static inline bool task_work_pending(struct task_struct *task)
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 2134ac8..5c2daa7 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -1,10 +1,18 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/irq_work.h>
 #include <linux/spinlock.h>
 #include <linux/task_work.h>
 #include <linux/resume_user_mode.h>
 
 static struct callback_head work_exited; /* all we need is ->next == NULL */
 
+static void task_work_set_notify_irq(struct irq_work *entry)
+{
+	test_and_set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+}
+static DEFINE_PER_CPU(struct irq_work, irq_work_NMI_resume) =
+	IRQ_WORK_INIT_HARD(task_work_set_notify_irq);
+
 /**
  * task_work_add - ask the @task to execute @work->func()
  * @task: the task which should run the callback
@@ -12,7 +20,7 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */
  * @notify: how to notify the targeted task
  *
  * Queue @work for task_work_run() below and notify the @task if @notify
- * is @TWA_RESUME, @TWA_SIGNAL, or @TWA_SIGNAL_NO_IPI.
+ * is @TWA_RESUME, @TWA_SIGNAL, @TWA_SIGNAL_NO_IPI or @TWA_NMI_CURRENT.
  *
  * @TWA_SIGNAL works like signals, in that the it will interrupt the targeted
  * task and run the task_work, regardless of whether the task is currently
@@ -24,6 +32,8 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */
  * kernel anyway.
  * @TWA_RESUME work is run only when the task exits the kernel and returns to
  * user mode, or before entering guest mode.
+ * @TWA_NMI_CURRENT works like @TWA_RESUME, except it can only be used for the
+ * current @task and if the current context is NMI.
  *
  * Fails if the @task is exiting/exited and thus it can't process this @work.
  * Otherwise @work->func() will be called when the @task goes through one of
@@ -44,8 +54,13 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 {
 	struct callback_head *head;
 
-	/* record the work call stack in order to print it in KASAN reports */
-	kasan_record_aux_stack(work);
+	if (notify == TWA_NMI_CURRENT) {
+		if (WARN_ON_ONCE(task != current))
+			return -EINVAL;
+	} else {
+		/* record the work call stack in order to print it in KASAN reports */
+		kasan_record_aux_stack(work);
+	}
 
 	head = READ_ONCE(task->task_works);
 	do {
@@ -66,6 +81,9 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 	case TWA_SIGNAL_NO_IPI:
 		__set_notify_signal(task);
 		break;
+	case TWA_NMI_CURRENT:
+		irq_work_queue(this_cpu_ptr(&irq_work_NMI_resume));
+		break;
 	default:
 		WARN_ON_ONCE(1);
 		break;

Patchew 2.1-devel-b67e4c2

© 2016 - 2025 Red Hat, Inc.