| From e8a4a2696fecb398b0288c43c0e0dbb91e265bb2 Mon Sep 17 00:00:00 2001 |
| From: Tahsin Erdogan <tahsin@google.com> |
| Date: Mon, 4 May 2015 21:15:31 -0700 |
| Subject: x86/spinlocks: Fix regression in spinlock contention detection |
| |
| From: Tahsin Erdogan <tahsin@google.com> |
| |
| 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@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 |
| Link: http://lkml.kernel.org/r/1430799331-20445-1-git-send-email-tahsin@google.com |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| 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 |
| |
