[Xen-devel] [PATCH] CPUIDLE: fix a racing in cpuidle_wakeup_mwait

["Wei, Gang" <gang.wei@xxxxxxxxx>]

CPUIDLE: fix a racing in cpuidle_wakeup_mwait

On 21/04/2010 10:52, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:
Oh, another one, which can **even occur without your patch**: CPU A adds
itself to cpuidle_mwait_flags while cpuidle_wakeup_mwait() is running. That
function doesn't see CPU A in its first read of the cpumask so it does not
set TIMER_SOFTIRQ for CPU A. But it then *does* see CPU A in its final read
of the cpumask, and hence clears A from the caller's mask. Hence the caller
does not pass CPU A to cpumask_raise_softirq(). Hence CPU A is erroneously
not woken.

Solution for it, just use the snapshot of cpuidle_mwait_flags in 
cpuidle_wakeup_mwait.

Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>

diff -r 57cabf99fd4d xen/arch/x86/acpi/cpu_idle.c
--- a/xen/arch/x86/acpi/cpu_idle.c      Wed Apr 21 14:32:31 2010 +0800
+++ b/xen/arch/x86/acpi/cpu_idle.c      Thu Apr 22 12:44:29 2010 +0800
@@ -169,7 +169,7 @@ void cpuidle_wakeup_mwait(cpumask_t *mas
     for_each_cpu_mask(cpu, target)
         set_bit(TIMER_SOFTIRQ, &softirq_pending(cpu));
 
-    cpus_andnot(*mask, *mask, cpuidle_mwait_flags);
+    cpus_andnot(*mask, *mask, target);
 }
 
 static void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)

Attachment: fix_mwait_wakeup.patch
Description: fix_mwait_wakeup.patch

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