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Commit e8a4a269 authored by Tahsin Erdogan's avatar Tahsin Erdogan Committed by Thomas Gleixner
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x86/spinlocks: Fix regression in spinlock contention detection



A spinlock is regarded as contended when there is at least one waiter.
Currently, the code that checks whether there are any waiters rely on
tail value being greater than head. However, this is not true if tail
reaches the max value and wraps back to zero, so arch_spin_is_contended()
incorrectly returns 0 (not contended) when tail is smaller than head.

The original code (before regression) handled this case by casting the
(tail - head) to an unsigned value. This change simply restores that
behavior.

Fixes: d6abfdb2 ("x86/spinlocks/paravirt: Fix memory corruption on unlock")
Signed-off-by: default avatarTahsin Erdogan <tahsin@google.com>
Cc: peterz@infradead.org
Cc: Waiman.Long@hp.com
Cc: borntraeger@de.ibm.com
Cc: oleg@redhat.com
Cc: raghavendra.kt@linux.vnet.ibm.com
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1430799331-20445-1-git-send-email-tahsin@google.com


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 94d4b476
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