From: Wanpeng Li <[email protected]>
When the lock holder vCPU is racing with the queue head:
CPU 0 (lock holder) CPU 1 (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 which can result in hash entry leak.
This patch avoids it by restoring/setting vcpu_hashed state after
failing adaptive locking spinning.
Reviewed-by: Pan Xinhui <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
v2 -> v3:
* fix typo in patch description
v1 -> v2:
* adjust patch description
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 21ede57..ac7d20b 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);
--
1.9.1
