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authorLinus Torvalds <torvalds@linux-foundation.org>2014-03-20 22:11:17 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-03-20 22:11:17 -0700
commit11d4616bd07f38d496bd489ed8fad1dc4d928823 (patch)
tree764239232ca4beac8797f274baf924e497f39151 /block
parent477cc48484ea0bfdee9e8319259b35a0ec03f332 (diff)
futex: revert back to the explicit waiter counting code
Srikar Dronamraju reports that commit b0c29f79ecea ("futexes: Avoid taking the hb->lock if there's nothing to wake up") causes java threads getting stuck on futexes when runing specjbb on a power7 numa box. The cause appears to be that the powerpc spinlocks aren't using the same ticket lock model that we use on x86 (and other) architectures, which in turn result in the "spin_is_locked()" test in hb_waiters_pending() occasionally reporting an unlocked spinlock even when there are pending waiters. So this reinstates Davidlohr Bueso's original explicit waiter counting code, which I had convinced Davidlohr to drop in favor of figuring out the pending waiters by just using the existing state of the spinlock and the wait queue. Reported-and-tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Original-code-by: Davidlohr Bueso <davidlohr@hp.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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