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lockmgr: avoid atomic on unlock in the slow path

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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.
This commit is contained in:
mjg 2018-05-18 22:57:52 +00:00
parent 27b7f19894
commit 9507177d38
1 changed files with 6 additions and 4 deletions
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10
sys/kern/kern_lock.c
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@ -132,8 +132,10 @@ 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
@ -1021,7 +1023,7 @@ lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_obje
* 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_int flags, struct lock_obje
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);