This is a note to let you know that I've just added the patch titled x86/spinlocks: Fix regression in spinlock contention detection to the 4.0-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-spinlocks-fix-regression-in-spinlock-contention-detection.patch and it can be found in the queue-4.0 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e8a4a2696fecb398b0288c43c0e0dbb91e265bb2 Mon Sep 17 00:00:00 2001 From: Tahsin Erdogan <tahsin@xxxxxxxxxx> Date: Mon, 4 May 2015 21:15:31 -0700 Subject: x86/spinlocks: Fix regression in spinlock contention detection From: Tahsin Erdogan <tahsin@xxxxxxxxxx> commit e8a4a2696fecb398b0288c43c0e0dbb91e265bb2 upstream. 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: d6abfdb20223 ("x86/spinlocks/paravirt: Fix memory corruption on unlock") Signed-off-by: Tahsin Erdogan <tahsin@xxxxxxxxxx> Cc: peterz@xxxxxxxxxxxxx Cc: Waiman.Long@xxxxxx Cc: borntraeger@xxxxxxxxxx Cc: oleg@xxxxxxxxxx Cc: raghavendra.kt@xxxxxxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/1430799331-20445-1-git-send-email-tahsin@xxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/spinlock.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -169,7 +169,7 @@ static inline int arch_spin_is_contended struct __raw_tickets tmp = READ_ONCE(lock->tickets); tmp.head &= ~TICKET_SLOWPATH_FLAG; - return (tmp.tail - tmp.head) > TICKET_LOCK_INC; + return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC; } #define arch_spin_is_contended arch_spin_is_contended Patches currently in stable-queue which might be from tahsin@xxxxxxxxxx are queue-4.0/x86-spinlocks-fix-regression-in-spinlock-contention-detection.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html