Date: Fri, 18 May 2018 22:57:52 +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: r333816 - head/sys/kern Message-ID: <201805182257.w4IMvqtG061416@repo.freebsd.org>
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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);
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