On Mon, 27 Aug 2007 16:06:19 +0100 (BST)
Hugh Dickins <[email protected]> wrote:
> Fix bogus DEBUG_PREEMPT warning on x86_64, when cpu brought online after
> bootup: current_is_keventd is right to note its use of smp_processor_id
> is preempt-safe, but should use raw_smp_processor_id to avoid the warning.
>
> Signed-off-by: Hugh Dickins <[email protected]>
>
> --- 2.6.23-rc3-git10/kernel/workqueue.c 2007-07-26 19:49:58.000000000 +0100
> +++ linux/kernel/workqueue.c 2007-08-26 18:59:16.000000000 +0100
> @@ -635,7 +635,7 @@ int keventd_up(void)
> int current_is_keventd(void)
> {
> struct cpu_workqueue_struct *cwq;
> - int cpu = smp_processor_id(); /* preempt-safe: keventd is per-cpu */
> + int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
> int ret = 0;
>
> BUG_ON(!keventd_wq);
But lib/smp_processor_id.c:debug_smp_processor_id() does
/*
* Kernel threads bound to a single CPU can safely use
* smp_processor_id():
*/
this_mask = cpumask_of_cpu(this_cpu);
if (cpus_equal(current->cpus_allowed, this_mask))
goto out;
So I assume that this warning was triggering because some non-keventd,
non-pinned task is calling current_is_keventd()?
So I agree with the patch, but not with its description.
-
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