Messages in this thread Patch in this message | | | Date | Wed, 10 Aug 2016 11:05:45 -0700 | From | tip-bot for Wanpeng Li <> | Subject | [tip:locking/core] locking/pvqspinlock: Fix double hash race |
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Commit-ID: 229ce631574761870a2ac938845fadbd07f35caa Gitweb: http://git.kernel.org/tip/229ce631574761870a2ac938845fadbd07f35caa Author: Wanpeng Li <wanpeng.li@hotmail.com> AuthorDate: Thu, 14 Jul 2016 16:15:56 +0800 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 10 Aug 2016 14:13:28 +0200
locking/pvqspinlock: Fix double hash race
When the lock holder vCPU is racing with the queue head:
CPU 0 (lock holder) CPU1 (queue head) =================== ================= spin_lock(); spin_lock(); pv_kick_node(): pv_wait_head_or_lock(): if (!lp) { lp = pv_hash(lock, pn); xchg(&l->locked, _Q_SLOW_VAL); } WRITE_ONCE(pn->state, vcpu_halted); cmpxchg(&pn->state, vcpu_halted, vcpu_hashed); WRITE_ONCE(l->locked, _Q_SLOW_VAL); (void)pv_hash(lock, pn);
In this case, lock holder inserts the pv_node of queue head into the hash table and set _Q_SLOW_VAL unnecessary. This patch avoids it by restoring/setting vcpu_hashed state after failing adaptive locking spinning.
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <Waiman.Long@hpe.com> Link: http://lkml.kernel.org/r/1468484156-4521-1-git-send-email-wanpeng.li@hotmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/locking/qspinlock_paravirt.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 37649e6..8a99abf 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -450,7 +450,7 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node) goto gotlock; } } - WRITE_ONCE(pn->state, vcpu_halted); + WRITE_ONCE(pn->state, vcpu_hashed); qstat_inc(qstat_pv_wait_head, true); qstat_inc(qstat_pv_wait_again, waitcnt); pv_wait(&l->locked, _Q_SLOW_VAL);
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