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/
