Messages in this thread | | | Date | Fri, 11 Dec 2015 06:17:47 -0800 | From | Davidlohr Bueso <> | Subject | Re: FW: Commit 81a43adae3b9 (locking/mutex: Use acquire/release semantics) causing failures on arm64 (ThunderX) |
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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
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