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Date:      Thu, 9 Feb 2017 08:19:30 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r313467 - head/sys/kern
Message-ID:  <201702090819.v198JUDj041822@repo.freebsd.org>
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Author: mjg
Date: Thu Feb  9 08:19:30 2017
New Revision: 313467
URL: https://svnweb.freebsd.org/changeset/base/313467

Log:
  locks: tidy up unlock fallback paths
  
  Update comments to note these functions are reachable if lockstat is
  enabled.
  
  Check if the lock has any bits set before attempting unlock, which saves
  an unnecessary atomic operation.

Modified:
  head/sys/kern/kern_mutex.c
  head/sys/kern/kern_rwlock.c
  head/sys/kern/kern_sx.c

Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c	Thu Feb  9 08:03:07 2017	(r313466)
+++ head/sys/kern/kern_mutex.c	Thu Feb  9 08:19:30 2017	(r313467)
@@ -853,25 +853,24 @@ thread_lock_set(struct thread *td, struc
 /*
  * __mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
  *
- * We are only called here if the lock is recursed or contested (i.e. we
- * need to wake up a blocked thread).
+ * We are only called here if the lock is recursed, contested (i.e. we
+ * need to wake up a blocked thread) or lockstat probe is active.
  */
 void
 __mtx_unlock_sleep(volatile uintptr_t *c, int opts, const char *file, int line)
 {
 	struct mtx *m;
 	struct turnstile *ts;
+	uintptr_t tid, v;
 
 	if (SCHEDULER_STOPPED())
 		return;
 
+	tid = (uintptr_t)curthread;
 	m = mtxlock2mtx(c);
+	v = MTX_READ_VALUE(m);
 
-	if (!mtx_recursed(m)) {
-		LOCKSTAT_PROFILE_RELEASE_LOCK(adaptive__release, m);
-		if (_mtx_release_lock(m, (uintptr_t)curthread))
-			return;
-	} else {
+	if (v & MTX_RECURSED) {
 		if (--(m->mtx_recurse) == 0)
 			atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
 		if (LOCK_LOG_TEST(&m->lock_object, opts))
@@ -879,6 +878,10 @@ __mtx_unlock_sleep(volatile uintptr_t *c
 		return;
 	}
 
+	LOCKSTAT_PROFILE_RELEASE_LOCK(adaptive__release, m);
+	if (v == tid && _mtx_release_lock(m, tid))
+		return;
+
 	/*
 	 * We have to lock the chain before the turnstile so this turnstile
 	 * can be removed from the hash list if it is empty.

Modified: head/sys/kern/kern_rwlock.c
==============================================================================
--- head/sys/kern/kern_rwlock.c	Thu Feb  9 08:03:07 2017	(r313466)
+++ head/sys/kern/kern_rwlock.c	Thu Feb  9 08:19:30 2017	(r313467)
@@ -1030,9 +1030,10 @@ __rw_wlock_hard(volatile uintptr_t *c, u
 }
 
 /*
- * This function is called if the first try at releasing a write lock failed.
- * This means that one of the 2 waiter bits must be set indicating that at
- * least one thread is waiting on this lock.
+ * This function is called if lockstat is active or the first try at releasing
+ * a write lock failed.  The latter means that the lock is recursed or one of
+ * the 2 waiter bits must be set indicating that at least one thread is waiting
+ * on this lock.
  */
 void
 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
@@ -1047,18 +1048,19 @@ __rw_wunlock_hard(volatile uintptr_t *c,
 		return;
 
 	rw = rwlock2rw(c);
-
-	if (!rw_recursed(rw)) {
-		LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw,
-		    LOCKSTAT_WRITER);
-		if (_rw_write_unlock(rw, tid))
-			return;
-	} else {
+	v = RW_READ_VALUE(rw);
+	if (v & RW_LOCK_WRITER_RECURSED) {
 		if (--(rw->rw_recurse) == 0)
 			atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
+		if (LOCK_LOG_TEST(&rw->lock_object, 0))
+			CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
 		return;
 	}
 
+	LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER);
+	if (v == tid && _rw_write_unlock(rw, tid))
+		return;
+
 	KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
 	    ("%s: neither of the waiter flags are set", __func__));
 

Modified: head/sys/kern/kern_sx.c
==============================================================================
--- head/sys/kern/kern_sx.c	Thu Feb  9 08:03:07 2017	(r313466)
+++ head/sys/kern/kern_sx.c	Thu Feb  9 08:19:30 2017	(r313467)
@@ -749,12 +749,8 @@ _sx_xunlock_hard(struct sx *sx, uintptr_
 
 	MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
 
-	if (!sx_recursed(sx)) {
-		LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx,
-		    LOCKSTAT_WRITER);
-		if (atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
-			return;
-	} else {
+	x = SX_READ_VALUE(sx);
+	if (x & SX_LOCK_RECURSED) {
 		/* The lock is recursed, unrecurse one level. */
 		if ((--sx->sx_recurse) == 0)
 			atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
@@ -762,6 +758,12 @@ _sx_xunlock_hard(struct sx *sx, uintptr_
 			CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 		return;
 	}
+
+	LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
+	if (x == tid &&
+	    atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
+		return;
+
 	MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
 	    SX_LOCK_EXCLUSIVE_WAITERS));
 	if (LOCK_LOG_TEST(&sx->lock_object, 0))

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