On Fri, Dec 11, 2015 at 6:18 AM, Davidlohr Bueso wrote: > > 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?
Yes that works for me. And yes that looks like the correct fix. >> >>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. Yes as mutex_optimistic_spin calls into osq_lock/osq_unlock. And 81a43adae3b9 changed mutex.c which David thought was where the issue was located rather than not what mutex_optimistic_spin called. Thanks, Andrew Pinski > > 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/
