Re: fix bogus hotplug cpu warning

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tue, 28 Aug 2007, Ingo Molnar wrote:
> this commit:
> 
>  commit d243769d3f83b318813a04a9592bb7cfedc6c280
>  Author: Hugh Dickins <[email protected]>
>  Date:   Mon Aug 27 16:06:19 2007 +0100
> 
>     fix bogus hotplug cpu warning
> 
>     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.
> 
> -       int cpu = smp_processor_id();   /* preempt-safe: keventd is per-cpu */
> +       int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
> 
> is incorrect. smp_processor_id() will _not_ warn about true per-cpu 
> tasks:
> 
>         /*
>          * 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 if this check triggered for the cpu-offline code it's because keventd 
> was _not_ per-cpu (perhaps because the cpu offline code broke its 
> affinity?). So your patch hides a real bug.

No, keventd is properly per-cpu, but the task which is calling
current_is_keventd() is a normal user task, so smp_processor_id()
did warn about it.  It wouldn't make much sense to have a function
current_is_keventd() if you could only call it from a keventd, would
it ;-?  Take a look at it (kernel/workqueue.c), I believe what it does
is unusual (hence that comment about being "preempt-safe") but valid.

Hugh
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux