x86: Fix mwait_play_dead() faulting on mwait-incapable cpus

A logic error in mwait_play_dead() causes the kernel to use
mwait even on cpus which don't support it, such as KVM virtual
cpus.

Introduced by:

  349c004e3d31: x86: A fast way to check capabilities of the current cpu

Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=36222
Reported-by: Török Edwin <edwintorok@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Link: http://lkml.kernel.org/r/1306758237-9327-1-git-send-email-avi@redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index eefd967..33a0c11 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1332,7 +1332,7 @@ static inline void mwait_play_dead(void)
        void *mwait_ptr;
        struct cpuinfo_x86 *c = __this_cpu_ptr(&cpu_info);
 
-       if (!this_cpu_has(X86_FEATURE_MWAIT) && mwait_usable(c))
+       if (!(this_cpu_has(X86_FEATURE_MWAIT) && mwait_usable(c)))
                return;
        if (!this_cpu_has(X86_FEATURE_CLFLSH))
                return;