Re: [PATCH v4 09/10] workqueue: Implement system-wide nr_active enforcement for unbound workqueues

[Marek Szyprowski]

On 31.01.2024 06:01, Tejun Heo wrote:
> From: Tejun Heo <tj@xxxxxxxxxx>
> Date: Tue, 30 Jan 2024 18:55:55 -1000
> Subject: [PATCH] workqueue: Don't call cpumask_test_cpu() with -1 CPU in
>   wq_update_node_max_active()
>
> For wq_update_node_max_active(), @off_cpu of -1 indicates that no CPU is
> going down. The function was incorrectly calling cpumask_test_cpu() with -1
> CPU leading to oopses like the following on some archs:
>
>    Unable to handle kernel paging request at virtual address ffff0002100296e0
>    ..
>    pc : wq_update_node_max_active+0x50/0x1fc
>    lr : wq_update_node_max_active+0x1f0/0x1fc
>    ...
>    Call trace:
>      wq_update_node_max_active+0x50/0x1fc
>      apply_wqattrs_commit+0xf0/0x114
>      apply_workqueue_attrs_locked+0x58/0xa0
>      alloc_workqueue+0x5ac/0x774
>      workqueue_init_early+0x460/0x540
>      start_kernel+0x258/0x684
>      __primary_switched+0xb8/0xc0
>    Code: 9100a273 35000d01 53067f00 d0016dc1 (f8607a60)
>    ---[ end trace 0000000000000000 ]---
>    Kernel panic - not syncing: Attempted to kill the idle task!
>    ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
>
> Fix it.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Link: http://lkml.kernel.org/r/91eacde0-df99-4d5c-a980-91046f66e612@xxxxxxxxxxx
> Fixes: 5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues")


Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>


> ---
> Applied to wq/for-6.9.
>
> Thanks.
>
>   kernel/workqueue.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 9221a4c57ae1..31c1373505d8 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1510,7 +1510,7 @@ static void wq_update_node_max_active(struct workqueue_struct *wq, int off_cpu)
>   
>   	lockdep_assert_held(&wq->mutex);
>   
> -	if (!cpumask_test_cpu(off_cpu, effective))
> +	if (off_cpu >= 0 && !cpumask_test_cpu(off_cpu, effective))
>   		off_cpu = -1;
>   
>   	total_cpus = cpumask_weight_and(effective, cpu_online_mask);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland