Re: [PATCH] workqueue: Make sure that wq_unbound_cpumask is never empty

[Tejun Heo]

On Tue, Nov 21, 2023 at 11:39:36AM -1000, Tejun Heo wrote:
> During boot, depending on how the housekeeping and workqueue.unbound_cpus
> masks are set, wq_unbound_cpumask can end up empty. Since 8639ecebc9b1
> ("workqueue: Implement non-strict affinity scope for unbound workqueues"),
> this may end up feeding -1 as a CPU number into scheduler leading to oopses.
> 
>   BUG: unable to handle page fault for address: ffffffff8305e9c0
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
>   ...
>   Call Trace:
>    <TASK>
>    select_idle_sibling+0x79/0xaf0
>    select_task_rq_fair+0x1cb/0x7b0
>    try_to_wake_up+0x29c/0x5c0
>    wake_up_process+0x19/0x20
>    kick_pool+0x5e/0xb0
>    __queue_work+0x119/0x430
>    queue_work_on+0x29/0x30
>   ...
> 
> An empty wq_unbound_cpumask is a clear misconfiguration and already
> disallowed once system is booted up. Let's warn on and ignore
> unbound_cpumask restrictions which lead to no unbound cpus. While at it,
> also remove now unncessary empty check on wq_unbound_cpumask in
> wq_select_unbound_cpu().
> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Reported-by: Yong He <alexyonghe@xxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/20231120121623.119780-1-alexyonghe@xxxxxxxxxxx
> Fixes: 8639ecebc9b1 ("workqueue: Implement non-strict affinity scope for unbound workqueues")
> Cc: stable@xxxxxxxxxxxxxxx # v6.6+

Applied to wq/for-6.7-fixes.

Thanks.

-- 
tejun