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author | Oleg Nesterov <oleg@redhat.com> | 2014-12-01 22:34:17 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2014-12-08 11:36:44 +0100 |
commit | 78bff1c8684fb94f1ae7283688f90188b53fc433 (patch) | |
tree | 48795bcb348947f7e213980570e7413dfc10fc3d /Documentation/locking | |
parent | 9fd7fc34cfcaf9f6c932ee1710cce83da3b7bd59 (diff) | |
download | op-kernel-dev-78bff1c8684fb94f1ae7283688f90188b53fc433.zip op-kernel-dev-78bff1c8684fb94f1ae7283688f90188b53fc433.tar.gz |
x86/ticketlock: Fix spin_unlock_wait() livelock
arch_spin_unlock_wait() looks very suboptimal, to the point I
think this is just wrong and can lead to livelock: if the lock
is heavily contended we can never see head == tail.
But we do not need to wait for arch_spin_is_locked() == F. If it
is locked we only need to wait until the current owner drops
this lock. So we could simply spin until old_head !=
lock->tickets.head in this case, but .head can overflow and thus
we can't check "unlocked" only once before the main loop.
Also, the "unlocked" check can ignore TICKET_SLOWPATH_FLAG bit.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Paul E.McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <Waiman.Long@hp.com>
Link: http://lkml.kernel.org/r/20141201213417.GA5842@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/locking')
0 files changed, 0 insertions, 0 deletions