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[PATCH v2 RESEND] tty/sysrq: replace smp_processor_id() with get_cpu()

Muhammad Usama Anjum posted 1 patch 2 years, 3 months ago
There is a newer version of this series
drivers/tty/sysrq.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
[PATCH v2 RESEND] tty/sysrq: replace smp_processor_id() with get_cpu()
Posted by Muhammad Usama Anjum 2 years, 3 months ago 
The smp_processor_id() shouldn't be called from preemptible code.
Instead use get_cpu() and put_cpu() which disables preemption in
addition to getting the processor id. This fixes the following bug:

[  119.143590] sysrq: Show backtrace of all active CPUs
[  119.143902] BUG: using smp_processor_id() in preemptible [00000000] code: bash/873
[  119.144586] caller is debug_smp_processor_id+0x20/0x30
[  119.144827] CPU: 6 PID: 873 Comm: bash Not tainted 5.10.124-dirty #3
[  119.144861] Hardware name: QEMU QEMU Virtual Machine, BIOS 2023.05-1 07/22/2023
[  119.145053] Call trace:
[  119.145093]  dump_backtrace+0x0/0x1a0
[  119.145122]  show_stack+0x18/0x70
[  119.145141]  dump_stack+0xc4/0x11c
[  119.145159]  check_preemption_disabled+0x100/0x110
[  119.145175]  debug_smp_processor_id+0x20/0x30
[  119.145195]  sysrq_handle_showallcpus+0x20/0xc0
[  119.145211]  __handle_sysrq+0x8c/0x1a0
[  119.145227]  write_sysrq_trigger+0x94/0x12c
[  119.145247]  proc_reg_write+0xa8/0xe4
[  119.145266]  vfs_write+0xec/0x280
[  119.145282]  ksys_write+0x6c/0x100
[  119.145298]  __arm64_sys_write+0x20/0x30
[  119.145315]  el0_svc_common.constprop.0+0x78/0x1e4
[  119.145332]  do_el0_svc+0x24/0x8c
[  119.145348]  el0_svc+0x10/0x20
[  119.145364]  el0_sync_handler+0x134/0x140
[  119.145381]  el0_sync+0x180/0x1c0

Cc: stable@vger.kernel.org
Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic arch fallback")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
---
Changes since v1:
- Add "Cc: stable@vger.kernel.org" tag
---
 drivers/tty/sysrq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 23198e3f1461a..6b4a28bcf2f5f 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -262,13 +262,14 @@ static void sysrq_handle_showallcpus(u8 key)
 		if (in_hardirq())
 			regs = get_irq_regs();
 
-		pr_info("CPU%d:\n", smp_processor_id());
+		pr_info("CPU%d:\n", get_cpu());
 		if (regs)
 			show_regs(regs);
 		else
 			show_stack(NULL, NULL, KERN_INFO);
 
 		schedule_work(&sysrq_showallcpus);
+		put_cpu();
 	}
 }
 
-- 
2.40.1
Re: [PATCH v2 RESEND] tty/sysrq: replace smp_processor_id() with get_cpu()
Posted by Greg Kroah-Hartman 2 years, 3 months ago 
On Tue, Aug 22, 2023 at 02:01:11PM +0500, Muhammad Usama Anjum wrote:
> The smp_processor_id() shouldn't be called from preemptible code.
> Instead use get_cpu() and put_cpu() which disables preemption in
> addition to getting the processor id. This fixes the following bug:
> 
> [  119.143590] sysrq: Show backtrace of all active CPUs
> [  119.143902] BUG: using smp_processor_id() in preemptible [00000000] code: bash/873
> [  119.144586] caller is debug_smp_processor_id+0x20/0x30
> [  119.144827] CPU: 6 PID: 873 Comm: bash Not tainted 5.10.124-dirty #3
> [  119.144861] Hardware name: QEMU QEMU Virtual Machine, BIOS 2023.05-1 07/22/2023
> [  119.145053] Call trace:
> [  119.145093]  dump_backtrace+0x0/0x1a0
> [  119.145122]  show_stack+0x18/0x70
> [  119.145141]  dump_stack+0xc4/0x11c
> [  119.145159]  check_preemption_disabled+0x100/0x110
> [  119.145175]  debug_smp_processor_id+0x20/0x30
> [  119.145195]  sysrq_handle_showallcpus+0x20/0xc0
> [  119.145211]  __handle_sysrq+0x8c/0x1a0
> [  119.145227]  write_sysrq_trigger+0x94/0x12c
> [  119.145247]  proc_reg_write+0xa8/0xe4
> [  119.145266]  vfs_write+0xec/0x280
> [  119.145282]  ksys_write+0x6c/0x100
> [  119.145298]  __arm64_sys_write+0x20/0x30
> [  119.145315]  el0_svc_common.constprop.0+0x78/0x1e4
> [  119.145332]  do_el0_svc+0x24/0x8c
> [  119.145348]  el0_svc+0x10/0x20
> [  119.145364]  el0_sync_handler+0x134/0x140
> [  119.145381]  el0_sync+0x180/0x1c0
> 
> Cc: stable@vger.kernel.org
> Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic arch fallback")
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> ---
> Changes since v1:
> - Add "Cc: stable@vger.kernel.org" tag
> ---

This is not a resend, it is a new version, v3.  Otherwise I would be
confused with the original v2 which is different than this one...

thanks,

greg k-h
Re: [PATCH v2 RESEND] tty/sysrq: replace smp_processor_id() with get_cpu()
Posted by Muhammad Usama Anjum 2 years, 3 months ago 
On 8/22/23 2:15 PM, Greg Kroah-Hartman wrote:
> On Tue, Aug 22, 2023 at 02:01:11PM +0500, Muhammad Usama Anjum wrote:
>> The smp_processor_id() shouldn't be called from preemptible code.
>> Instead use get_cpu() and put_cpu() which disables preemption in
>> addition to getting the processor id. This fixes the following bug:
>>
>> [  119.143590] sysrq: Show backtrace of all active CPUs
>> [  119.143902] BUG: using smp_processor_id() in preemptible [00000000] code: bash/873
>> [  119.144586] caller is debug_smp_processor_id+0x20/0x30
>> [  119.144827] CPU: 6 PID: 873 Comm: bash Not tainted 5.10.124-dirty #3
>> [  119.144861] Hardware name: QEMU QEMU Virtual Machine, BIOS 2023.05-1 07/22/2023
>> [  119.145053] Call trace:
>> [  119.145093]  dump_backtrace+0x0/0x1a0
>> [  119.145122]  show_stack+0x18/0x70
>> [  119.145141]  dump_stack+0xc4/0x11c
>> [  119.145159]  check_preemption_disabled+0x100/0x110
>> [  119.145175]  debug_smp_processor_id+0x20/0x30
>> [  119.145195]  sysrq_handle_showallcpus+0x20/0xc0
>> [  119.145211]  __handle_sysrq+0x8c/0x1a0
>> [  119.145227]  write_sysrq_trigger+0x94/0x12c
>> [  119.145247]  proc_reg_write+0xa8/0xe4
>> [  119.145266]  vfs_write+0xec/0x280
>> [  119.145282]  ksys_write+0x6c/0x100
>> [  119.145298]  __arm64_sys_write+0x20/0x30
>> [  119.145315]  el0_svc_common.constprop.0+0x78/0x1e4
>> [  119.145332]  do_el0_svc+0x24/0x8c
>> [  119.145348]  el0_svc+0x10/0x20
>> [  119.145364]  el0_sync_handler+0x134/0x140
>> [  119.145381]  el0_sync+0x180/0x1c0
>>
>> Cc: stable@vger.kernel.org
>> Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic arch fallback")
>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
>> ---
>> Changes since v1:
>> - Add "Cc: stable@vger.kernel.org" tag
>> ---
> 
> This is not a resend, it is a new version, v3.  Otherwise I would be
> confused with the original v2 which is different than this one...
Sorry, didn't relaize this. I've sent this as v3:
https://lore.kernel.org/all/20230822102606.2821311-1-usama.anjum@collabora.com

> 
> thanks,
> 
> greg k-h

-- 
BR,
Muhammad Usama Anjum

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