Will Deacon 38b850a730 arm64: spinlock: order spin_{is_locked,unlock_wait} against local locks ... spin_is_locked has grown two very different use-cases: (1) [The sane case] API functions may require a certain lock to be held by the caller and can therefore use spin_is_locked as part of an assert statement in order to verify that the lock is indeed held. For example, usage of assert_spin_locked. (2) [The insane case] There are two locks, where a CPU takes one of the locks and then checks whether or not the other one is held before accessing some shared state. For example, the "optimized locking" in ipc/sem.c. In the latter case, the sequence looks like: spin_lock(&sem->lock); if (!spin_is_locked(&sma->sem_perm.lock)) /* Access shared state */ and requires that the spin_is_locked check is ordered after taking the sem->lock. Unfortunately, since our spinlocks are implemented using a LDAXR/STXR sequence, the read of &sma->sem_perm.lock can be speculated before the STXR and consequently return a stale value. Whilst this hasn't been seen to cause issues in practice, PowerPC fixed the same issue in 51d7d5205d ("powerpc: Add smp_mb() to arch_spin_is_locked()") and, although we did something similar for spin_unlock_wait in d86b8da04d ("arm64: spinlock: serialise spin_unlock_wait against concurrent lockers") that doesn't actually take care of ordering against local acquisition of a different lock. This patch adds an smp_mb() to the start of our arch_spin_is_locked and arch_spin_unlock_wait routines to ensure that the lock value is always loaded after any other locks have been taken by the current CPU. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Will Deacon <will.deacon@arm.com>		2016-06-15 09:51:35 +01:00
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asm	arm64: spinlock: order spin_{is_locked,unlock_wait} against local locks	2016-06-15 09:51:35 +01:00
uapi/asm	asm-generic: Drop renameat syscall from default list	2016-05-05 00:42:21 +02:00