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: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 Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1430799331-20445-1-git-send-email-tahsin@google.com Signed-off-by:
Thomas Gleixner <tglx@linutronix.de>
parent
94d4b476
Please register or sign in to comment