locking/pvqspinlock: Order pv_unhash() after cmpxchg() on unlock slowpath
When we unlock in __pv_queued_spin_unlock(), a failed cmpxchg() on the lock value indicates that we need to take the slow-path and unhash the corresponding node blocked on the lock. Since a failed cmpxchg() does not provide any memory-ordering guarantees, it is possible that the node data could be read before the cmpxchg() on weakly-ordered architectures and therefore return a stale value, leading to hash corruption and/or a BUG(). This patch adds an smb_rmb() following the failed cmpxchg operation, so that the unhashing is ordered after the lock has been checked. Reported-by:Peter Zijlstra <peterz@infradead.org> Signed-off-by:
Will Deacon <will.deacon@arm.com> [ Added more comments] Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by:
Waiman Long <Waiman.Long@hp.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul McKenney <paulmck@linux.vnet.ibm.com> Cc: Steve Capper <Steve.Capper@arm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20150713155830.GL2632@arm.com Signed-off-by:
Ingo Molnar <mingo@kernel.org>
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