Merge tag 'drm-fixes-for-v4.9-rc2' of git://people.freedesktop.org/~airlied/linux

[cascardo/linux.git] / kernel / locking / qspinlock_paravirt.h

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 8a99abf..e3b5520 100644 (file)
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -70,11 +70,14 @@ struct pv_node {
 static inline bool pv_queued_spin_steal_lock(struct qspinlock *lock)
 {
        struct __qspinlock *l = (void *)lock;
-       int ret = !(atomic_read(&lock->val) & _Q_LOCKED_PENDING_MASK) &&
-                  (cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0);
 
-       qstat_inc(qstat_pv_lock_stealing, ret);
-       return ret;
+       if (!(atomic_read(&lock->val) & _Q_LOCKED_PENDING_MASK) &&
+           (cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0)) {
+               qstat_inc(qstat_pv_lock_stealing, true);
+               return true;
+       }
+
+       return false;
 }
 
 /*
@@ -257,7 +260,6 @@ static struct pv_node *pv_unhash(struct qspinlock *lock)
 static inline bool
 pv_wait_early(struct pv_node *prev, int loop)
 {
-
        if ((loop & PV_PREV_CHECK_MASK) != 0)
                return false;
 
@@ -286,12 +288,10 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 {
        struct pv_node *pn = (struct pv_node *)node;
        struct pv_node *pp = (struct pv_node *)prev;
-       int waitcnt = 0;
        int loop;
        bool wait_early;
 
-       /* waitcnt processing will be compiled out if !QUEUED_LOCK_STAT */
-       for (;; waitcnt++) {
+       for (;;) {
                for (wait_early = false, loop = SPIN_THRESHOLD; loop; loop--) {
                        if (READ_ONCE(node->locked))
                                return;
@@ -315,7 +315,6 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
 
                if (!READ_ONCE(node->locked)) {
                        qstat_inc(qstat_pv_wait_node, true);
-                       qstat_inc(qstat_pv_wait_again, waitcnt);
                        qstat_inc(qstat_pv_wait_early, wait_early);
                        pv_wait(&pn->state, vcpu_halted);
                }
@@ -456,12 +455,9 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
                pv_wait(&l->locked, _Q_SLOW_VAL);
 
                /*
-                * The unlocker should have freed the lock before kicking the
-                * CPU. So if the lock is still not free, it is a spurious
-                * wakeup or another vCPU has stolen the lock. The current
-                * vCPU should spin again.
+                * Because of lock stealing, the queue head vCPU may not be
+                * able to acquire the lock before it has to wait again.
                 */
-               qstat_inc(qstat_pv_spurious_wakeup, READ_ONCE(l->locked));
        }
 
        /*
@@ -544,7 +540,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
         * unhash. Otherwise it would be possible to have multiple @lock
         * entries, which would be BAD.
         */
-       locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+       locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
        if (likely(locked == _Q_LOCKED_VAL))
                return;