On Fri, 11 Dec 2015, Will Deacon wrote:
I think Andrew meant the atomic_xchg_acquire at the start of osq_lock, as opposed to "compare and swap". In which case, it does look like there's a bug here because there is nothing to order the initialisation of the node fields with publishing of the node, whether that's indirectly as a result of setting the tail to the current CPU or directly as a result of the WRITE_ONCE.
Sorry I'm late to the party. Duh yes this is obviously bogus, and worse I recall triggering a similar tail initialization issue in osq_lock on some experimental work on x86, so this is very much a point of failure. Ack.
Andrew, David: does making that atomic_xchg_acquire and atomic_xchg fix things for you? I don't fully grok what 81a43adae3b9 has to do with any of this, so maybe there's another bug too.
I think this is mainly because mutex_optimistic_spin is where the stack shows the lockup, which really translates to c55a6ffa62. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
