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SubjectRe: linux-next: tracebacks in workqueue.c/__flush_work()
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Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> writes:
> (Adding Chris Metcalf and Rusty Russell.)
>
> If NR_CPUS == 1 due to CONFIG_SMP=n, for_each_cpu(cpu, &has_work) loop does not
> evaluate "struct cpumask has_work" modified by cpumask_set_cpu(cpu, &has_work) at
> previous for_each_online_cpu() loop. Guenter Roeck found a problem among three
> commits listed below.
>
> Commit 5fbc461636c32efd ("mm: make lru_add_drain_all() selective")
> expects that has_work is evaluated by for_each_cpu().
>
> Commit 2d3854a37e8b767a ("cpumask: introduce new API, without changing anything")
> assumes that for_each_cpu() does not need to evaluate has_work.
>
> Commit 4d43d395fed12463 ("workqueue: Try to catch flush_work() without INIT_WORK().")
> expects that has_work is evaluated by for_each_cpu().
>
> What should we do? Do we explicitly evaluate has_mask if NR_CPUS == 1 ?

No, fix the API to be least-surprise. Fix 2d3854a37e8b767a too.

Doing anything else would be horrible, IMHO.

Cheers,
Rusty.

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