Commit-ID: 229ce631574761870a2ac938845fadbd07f35caa
Gitweb: http://git.kernel.org/tip/229ce631574761870a2ac938845fadbd07f35caa
Author: Wanpeng Li <wanpeng...@hotmail.com>
AuthorDate: Thu, 14 Jul 2016 16:15:56 +0800
Committer: Ingo Molnar <mi...@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...@hotmail.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Reviewed-by: Pan Xinhui <xinhui....@linux.vnet.ibm.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Waiman Long <waiman.l...@hpe.com>
Link:
http://lkml.kernel.org/r/1468484156-4521-1-git-send-email-wanpeng...@hotmail.com
Signed-off-by: Ingo Molnar <mi...@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);
