Author: mjg
Date: Fri May 18 22:57:52 2018
New Revision: 333816
URL: https://svnweb.freebsd.org/changeset/base/333816
Log:
lockmgr: avoid atomic on unlock in the slow path
The code is pretty much guaranteed not to be able to unlock.
This is a minor nit. The code still performs way too many reads.
The altered exclusive-locked condition is supposed to be always
true as well, to be cleaned up at a later date.
Modified:
head/sys/kern/kern_lock.c
Modified: head/sys/kern/kern_lock.c
==============================================================================
--- head/sys/kern/kern_lock.c Fri May 18 22:22:08 2018 (r333815)
+++ head/sys/kern/kern_lock.c Fri May 18 22:57:52 2018 (r333816)
@@ -132,9 +132,11 @@ CTASSERT(LK_UNLOCKED == (LK_UNLOCKED &
#define lockmgr_disowned(lk)
\
(((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC)
-#define lockmgr_xlocked(lk)
\
- (((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread)
+#define lockmgr_xlocked_v(v)
\
+ (((v) & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread)
+#define lockmgr_xlocked(lk) lockmgr_xlocked_v((lk)->lk_lock)
+
static void assert_lockmgr(const struct lock_object *lock, int how);
#ifdef DDB
static void db_show_lockmgr(const struct lock_object *lock);
@@ -1021,7 +1023,7 @@ lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_i
* The lock is held in exclusive mode.
* If the lock is recursed also, then unrecurse it.
*/
- if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) {
+ if (lockmgr_xlocked_v(x) && lockmgr_recursed(lk)) {
LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk);
lk->lk_recurse--;
goto out;
@@ -1029,7 +1031,7 @@ lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_i
if (tid != LK_KERNPROC)
lock_profile_release_lock(&lk->lock_object);
- if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED))
+ if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED))
goto out;
sleepq_lock(&lk->lock_object);
_______________________________________________
svn-src-head@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
