/*- * Copyright (c) 2008 Attilio Rao * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice(s), this list of conditions and the following disclaimer as * the first lines of this file unmodified other than the possible * addition of one or more copyright notices. * 2. Redistributions in binary form must reproduce the above copyright * notice(s), this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH * DAMAGE. */ #include "opt_adaptive_lockmgrs.h" #include "opt_ddb.h" #include "opt_kdtrace.h" #include __FBSDID("$FreeBSD$"); #include #include #include #include #include #include #include #include #ifdef DEBUG_LOCKS #include #endif #include #include #include #ifdef DDB #include #endif CTASSERT(((LK_ADAPTIVE | LK_NOSHARE) & LO_CLASSFLAGS) == (LK_ADAPTIVE | LK_NOSHARE)); CTASSERT(LK_UNLOCKED == (LK_UNLOCKED & ~(LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS))); #define SQ_EXCLUSIVE_QUEUE 0 #define SQ_SHARED_QUEUE 1 #ifndef INVARIANTS #define _lockmgr_assert(lk, what, file, line) #define TD_LOCKS_INC(td) #define TD_LOCKS_DEC(td) #else #define TD_LOCKS_INC(td) ((td)->td_locks++) #define TD_LOCKS_DEC(td) ((td)->td_locks--) #endif #define TD_SLOCKS_INC(td) ((td)->td_lk_slocks++) #define TD_SLOCKS_DEC(td) ((td)->td_lk_slocks--) #ifndef DEBUG_LOCKS #define STACK_PRINT(lk) #define STACK_SAVE(lk) #define STACK_ZERO(lk) #else #define STACK_PRINT(lk) stack_print_ddb(&(lk)->lk_stack) #define STACK_SAVE(lk) stack_save(&(lk)->lk_stack) #define STACK_ZERO(lk) stack_zero(&(lk)->lk_stack) #endif #define LOCK_LOG2(lk, string, arg1, arg2) \ if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \ CTR2(KTR_LOCK, (string), (arg1), (arg2)) #define LOCK_LOG3(lk, string, arg1, arg2, arg3) \ if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \ CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3)) #define GIANT_DECLARE \ int _i = 0; \ WITNESS_SAVE_DECL(Giant) #define GIANT_RESTORE() do { \ if (_i > 0) { \ while (_i--) \ mtx_lock(&Giant); \ WITNESS_RESTORE(&Giant.lock_object, Giant); \ } \ } while (0) #define GIANT_SAVE() do { \ if (mtx_owned(&Giant)) { \ WITNESS_SAVE(&Giant.lock_object, Giant); \ while (mtx_owned(&Giant)) { \ _i++; \ mtx_unlock(&Giant); \ } \ } \ } while (0) #define LK_CAN_SHARE(x) \ (((x) & LK_SHARE) && (((x) & LK_EXCLUSIVE_WAITERS) == 0 || \ ((x) & LK_EXCLUSIVE_SPINNERS) == 0 || \ curthread->td_lk_slocks || (curthread->td_pflags & TDP_DEADLKTREAT))) #define LK_TRYOP(x) \ ((x) & LK_NOWAIT) #define LK_CAN_WITNESS(x) \ (((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x)) #define LK_TRYWIT(x) \ (LK_TRYOP(x) ? LOP_TRYLOCK : 0) #define LK_CAN_ADAPT(lk, f) \ (((lk)->lock_object.lo_flags & LK_ADAPTIVE) != 0 && \ ((f) & LK_SLEEPFAIL) == 0) #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) static void assert_lockmgr(const struct lock_object *lock, int how); #ifdef DDB static void db_show_lockmgr(const struct lock_object *lock); #endif static void lock_lockmgr(struct lock_object *lock, int how); #ifdef KDTRACE_HOOKS static int owner_lockmgr(const struct lock_object *lock, struct thread **owner); #endif static int unlock_lockmgr(struct lock_object *lock); struct lock_class lock_class_lockmgr = { .lc_name = "lockmgr", .lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE, .lc_assert = assert_lockmgr, #ifdef DDB .lc_ddb_show = db_show_lockmgr, #endif .lc_lock = lock_lockmgr, .lc_unlock = unlock_lockmgr, #ifdef KDTRACE_HOOKS .lc_owner = owner_lockmgr, #endif }; #ifdef ADAPTIVE_LOCKMGRS static u_int alk_retries = 10; static u_int alk_loops = 10000; static SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL, "lockmgr debugging"); SYSCTL_UINT(_debug_lockmgr, OID_AUTO, retries, CTLFLAG_RW, &alk_retries, 0, ""); SYSCTL_UINT(_debug_lockmgr, OID_AUTO, loops, CTLFLAG_RW, &alk_loops, 0, ""); #endif static __inline struct thread * lockmgr_xholder(const struct lock *lk) { uintptr_t x; x = lk->lk_lock; return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x)); } /* * It assumes sleepq_lock held and returns with this one unheld. * It also assumes the generic interlock is sane and previously checked. * If LK_INTERLOCK is specified the interlock is not reacquired after the * sleep. */ static __inline int sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk, const char *wmesg, int pri, int timo, int queue) { GIANT_DECLARE; struct lock_class *class; int catch, error; class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL; catch = pri & PCATCH; pri &= PRIMASK; error = 0; LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk, (queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared"); if (flags & LK_INTERLOCK) class->lc_unlock(ilk); if (queue == SQ_EXCLUSIVE_QUEUE && (flags & LK_SLEEPFAIL) != 0) lk->lk_exslpfail++; GIANT_SAVE(); sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ? SLEEPQ_INTERRUPTIBLE : 0), queue); if ((flags & LK_TIMELOCK) && timo) sleepq_set_timeout(&lk->lock_object, timo); /* * Decisional switch for real sleeping. */ if ((flags & LK_TIMELOCK) && timo && catch) error = sleepq_timedwait_sig(&lk->lock_object, pri); else if ((flags & LK_TIMELOCK) && timo) error = sleepq_timedwait(&lk->lock_object, pri); else if (catch) error = sleepq_wait_sig(&lk->lock_object, pri); else sleepq_wait(&lk->lock_object, pri); GIANT_RESTORE(); if ((flags & LK_SLEEPFAIL) && error == 0) error = ENOLCK; return (error); } static __inline int wakeupshlk(struct lock *lk, const char *file, int line) { uintptr_t v, x; u_int realexslp; int queue, wakeup_swapper; TD_LOCKS_DEC(curthread); TD_SLOCKS_DEC(curthread); WITNESS_UNLOCK(&lk->lock_object, 0, file, line); LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line); wakeup_swapper = 0; for (;;) { x = lk->lk_lock; /* * If there is more than one shared lock held, just drop one * and return. */ if (LK_SHARERS(x) > 1) { if (atomic_cmpset_rel_ptr(&lk->lk_lock, x, x - LK_ONE_SHARER)) break; continue; } /* * If there are not waiters on the exclusive queue, drop the * lock quickly. */ if ((x & LK_ALL_WAITERS) == 0) { MPASS((x & ~LK_EXCLUSIVE_SPINNERS) == LK_SHARERS_LOCK(1)); if (atomic_cmpset_rel_ptr(&lk->lk_lock, x, LK_UNLOCKED)) break; continue; } /* * We should have a sharer with waiters, so enter the hard * path in order to handle wakeups correctly. */ sleepq_lock(&lk->lock_object); x = lk->lk_lock & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); v = LK_UNLOCKED; /* * If the lock has exclusive waiters, give them preference in * order to avoid deadlock with shared runners up. * If interruptible sleeps left the exclusive queue empty * avoid a starvation for the threads sleeping on the shared * queue by giving them precedence and cleaning up the * exclusive waiters bit anyway. * Please note that lk_exslpfail count may be lying about * the real number of waiters with the LK_SLEEPFAIL flag on * because they may be used in conjuction with interruptible * sleeps so lk_exslpfail might be considered an 'upper limit' * bound, including the edge cases. */ realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE); if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) { if (lk->lk_exslpfail < realexslp) { lk->lk_exslpfail = 0; queue = SQ_EXCLUSIVE_QUEUE; v |= (x & LK_SHARED_WAITERS); } else { lk->lk_exslpfail = 0; LOCK_LOG2(lk, "%s: %p has only LK_SLEEPFAIL sleepers", __func__, lk); LOCK_LOG2(lk, "%s: %p waking up threads on the exclusive queue", __func__, lk); wakeup_swapper = sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE); queue = SQ_SHARED_QUEUE; } } else { /* * Exclusive waiters sleeping with LK_SLEEPFAIL on * and using interruptible sleeps/timeout may have * left spourious lk_exslpfail counts on, so clean * it up anyway. */ lk->lk_exslpfail = 0; queue = SQ_SHARED_QUEUE; } if (!atomic_cmpset_rel_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x, v)) { sleepq_release(&lk->lock_object); continue; } LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue", __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : "exclusive"); wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue); sleepq_release(&lk->lock_object); break; } lock_profile_release_lock(&lk->lock_object); return (wakeup_swapper); } static void assert_lockmgr(const struct lock_object *lock, int what) { panic("lockmgr locks do not support assertions"); } static void lock_lockmgr(struct lock_object *lock, int how) { panic("lockmgr locks do not support sleep interlocking"); } static int unlock_lockmgr(struct lock_object *lock) { panic("lockmgr locks do not support sleep interlocking"); } #ifdef KDTRACE_HOOKS static int owner_lockmgr(const struct lock_object *lock, struct thread **owner) { panic("lockmgr locks do not support owner inquiring"); } #endif void lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags) { int iflags; MPASS((flags & ~LK_INIT_MASK) == 0); ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock, ("%s: lockmgr not aligned for %s: %p", __func__, wmesg, &lk->lk_lock)); iflags = LO_SLEEPABLE | LO_UPGRADABLE; if (flags & LK_CANRECURSE) iflags |= LO_RECURSABLE; if ((flags & LK_NODUP) == 0) iflags |= LO_DUPOK; if (flags & LK_NOPROFILE) iflags |= LO_NOPROFILE; if ((flags & LK_NOWITNESS) == 0) iflags |= LO_WITNESS; if (flags & LK_QUIET) iflags |= LO_QUIET; iflags |= flags & (LK_ADAPTIVE | LK_NOSHARE); lk->lk_lock = LK_UNLOCKED; lk->lk_recurse = 0; lk->lk_exslpfail = 0; lk->lk_timo = timo; lk->lk_pri = pri; lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags); STACK_ZERO(lk); } /* * XXX: Gross hacks to manipulate external lock flags after * initialization. Used for certain vnode and buf locks. */ void lockallowshare(struct lock *lk) { lockmgr_assert(lk, KA_XLOCKED); lk->lock_object.lo_flags &= ~LK_NOSHARE; } void lockallowrecurse(struct lock *lk) { lockmgr_assert(lk, KA_XLOCKED); lk->lock_object.lo_flags |= LO_RECURSABLE; } void lockdisablerecurse(struct lock *lk) { lockmgr_assert(lk, KA_XLOCKED); lk->lock_object.lo_flags &= ~LO_RECURSABLE; } void lockdestroy(struct lock *lk) { KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held")); KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed")); KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters")); lock_destroy(&lk->lock_object); } int __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk, const char *wmesg, int pri, int timo, const char *file, int line) { GIANT_DECLARE; struct lock_class *class; const char *iwmesg; uintptr_t tid, v, x; u_int op, realexslp; int error, ipri, itimo, queue, wakeup_swapper; #ifdef LOCK_PROFILING uint64_t waittime = 0; int contested = 0; #endif #ifdef ADAPTIVE_LOCKMGRS volatile struct thread *owner; u_int i, spintries = 0; #endif error = 0; tid = (uintptr_t)curthread; op = (flags & LK_TYPE_MASK); iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg; ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri; itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo; MPASS((flags & ~LK_TOTAL_MASK) == 0); KASSERT((op & (op - 1)) == 0, ("%s: Invalid requested operation @ %s:%d", __func__, file, line)); KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 || (op != LK_DOWNGRADE && op != LK_RELEASE), ("%s: Invalid flags in regard of the operation desired @ %s:%d", __func__, file, line)); KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL, ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d", __func__, file, line)); class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL; if (panicstr != NULL) { if (flags & LK_INTERLOCK) class->lc_unlock(ilk); return (0); } if (lk->lock_object.lo_flags & LK_NOSHARE) { switch (op) { case LK_SHARED: op = LK_EXCLUSIVE; break; case LK_UPGRADE: case LK_DOWNGRADE: _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line); return (0); } } wakeup_swapper = 0; switch (op) { case LK_SHARED: if (LK_CAN_WITNESS(flags)) WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, file, line, ilk); for (;;) { x = lk->lk_lock; /* * If no other thread has an exclusive lock, or * no exclusive waiter is present, bump the count of * sharers. Since we have to preserve the state of * waiters, if we fail to acquire the shared lock * loop back and retry. */ if (LK_CAN_SHARE(x)) { if (atomic_cmpset_acq_ptr(&lk->lk_lock, x, x + LK_ONE_SHARER)) break; continue; } lock_profile_obtain_lock_failed(&lk->lock_object, &contested, &waittime); /* * If the lock is already held by curthread in * exclusive way avoid a deadlock. */ if (LK_HOLDER(x) == tid) { LOCK_LOG2(lk, "%s: %p already held in exclusive mode", __func__, lk); error = EDEADLK; break; } /* * If the lock is expected to not sleep just give up * and return. */ if (LK_TRYOP(flags)) { LOCK_LOG2(lk, "%s: %p fails the try operation", __func__, lk); error = EBUSY; break; } #ifdef ADAPTIVE_LOCKMGRS /* * If the owner is running on another CPU, spin until * the owner stops running or the state of the lock * changes. We need a double-state handle here * because for a failed acquisition the lock can be * either held in exclusive mode or shared mode * (for the writer starvation avoidance technique). */ if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 && LK_HOLDER(x) != LK_KERNPROC) { owner = (struct thread *)LK_HOLDER(x); if (LOCK_LOG_TEST(&lk->lock_object, 0)) CTR3(KTR_LOCK, "%s: spinning on %p held by %p", __func__, lk, owner); /* * If we are holding also an interlock drop it * in order to avoid a deadlock if the lockmgr * owner is adaptively spinning on the * interlock itself. */ if (flags & LK_INTERLOCK) { class->lc_unlock(ilk); flags &= ~LK_INTERLOCK; } GIANT_SAVE(); while (LK_HOLDER(lk->lk_lock) == (uintptr_t)owner && TD_IS_RUNNING(owner)) cpu_spinwait(); GIANT_RESTORE(); continue; } else if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) != 0 && LK_SHARERS(x) && spintries < alk_retries) { if (flags & LK_INTERLOCK) { class->lc_unlock(ilk); flags &= ~LK_INTERLOCK; } GIANT_SAVE(); spintries++; for (i = 0; i < alk_loops; i++) { if (LOCK_LOG_TEST(&lk->lock_object, 0)) CTR4(KTR_LOCK, "%s: shared spinning on %p with %u and %u", __func__, lk, spintries, i); x = lk->lk_lock; if ((x & LK_SHARE) == 0 || LK_CAN_SHARE(x) != 0) break; cpu_spinwait(); } GIANT_RESTORE(); if (i != alk_loops) continue; } #endif /* * Acquire the sleepqueue chain lock because we * probabilly will need to manipulate waiters flags. */ sleepq_lock(&lk->lock_object); x = lk->lk_lock; /* * if the lock can be acquired in shared mode, try * again. */ if (LK_CAN_SHARE(x)) { sleepq_release(&lk->lock_object); continue; } #ifdef ADAPTIVE_LOCKMGRS /* * The current lock owner might have started executing * on another CPU (or the lock could have changed * owner) while we were waiting on the turnstile * chain lock. If so, drop the turnstile lock and try * again. */ if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 && LK_HOLDER(x) != LK_KERNPROC) { owner = (struct thread *)LK_HOLDER(x); if (TD_IS_RUNNING(owner)) { sleepq_release(&lk->lock_object); continue; } } #endif /* * Try to set the LK_SHARED_WAITERS flag. If we fail, * loop back and retry. */ if ((x & LK_SHARED_WAITERS) == 0) { if (!atomic_cmpset_acq_ptr(&lk->lk_lock, x, x | LK_SHARED_WAITERS)) { sleepq_release(&lk->lock_object); continue; } LOCK_LOG2(lk, "%s: %p set shared waiters flag", __func__, lk); } /* * As far as we have been unable to acquire the * shared lock and the shared waiters flag is set, * we will sleep. */ error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo, SQ_SHARED_QUEUE); flags &= ~LK_INTERLOCK; if (error) { LOCK_LOG3(lk, "%s: interrupted sleep for %p with %d", __func__, lk, error); break; } LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", __func__, lk); } if (error == 0) { lock_profile_obtain_lock_success(&lk->lock_object, contested, waittime, file, line); LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file, line); WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file, line); TD_LOCKS_INC(curthread); TD_SLOCKS_INC(curthread); STACK_SAVE(lk); } break; case LK_UPGRADE: _lockmgr_assert(lk, KA_SLOCKED, file, line); v = lk->lk_lock; x = v & LK_ALL_WAITERS; v &= LK_EXCLUSIVE_SPINNERS; /* * Try to switch from one shared lock to an exclusive one. * We need to preserve waiters flags during the operation. */ if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x | v, tid | x)) { LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file, line); WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file, line); TD_SLOCKS_DEC(curthread); break; } /* * We have been unable to succeed in upgrading, so just * give up the shared lock. */ wakeup_swapper |= wakeupshlk(lk, file, line); /* FALLTHROUGH */ case LK_EXCLUSIVE: if (LK_CAN_WITNESS(flags)) WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, line, ilk); /* * If curthread already holds the lock and this one is * allowed to recurse, simply recurse on it. */ if (lockmgr_xlocked(lk)) { if ((flags & LK_CANRECURSE) == 0 && (lk->lock_object.lo_flags & LO_RECURSABLE) == 0) { /* * If the lock is expected to not panic just * give up and return. */ if (LK_TRYOP(flags)) { LOCK_LOG2(lk, "%s: %p fails the try operation", __func__, lk); error = EBUSY; break; } if (flags & LK_INTERLOCK) class->lc_unlock(ilk); panic("%s: recursing on non recursive lockmgr %s @ %s:%d\n", __func__, iwmesg, file, line); } lk->lk_recurse++; LOCK_LOG2(lk, "%s: %p recursing", __func__, lk); LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line); WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file, line); TD_LOCKS_INC(curthread); break; } while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) { lock_profile_obtain_lock_failed(&lk->lock_object, &contested, &waittime); /* * If the lock is expected to not sleep just give up * and return. */ if (LK_TRYOP(flags)) { LOCK_LOG2(lk, "%s: %p fails the try operation", __func__, lk); error = EBUSY; break; } #ifdef ADAPTIVE_LOCKMGRS /* * If the owner is running on another CPU, spin until * the owner stops running or the state of the lock * changes. */ x = lk->lk_lock; if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 && LK_HOLDER(x) != LK_KERNPROC) { owner = (struct thread *)LK_HOLDER(x); if (LOCK_LOG_TEST(&lk->lock_object, 0)) CTR3(KTR_LOCK, "%s: spinning on %p held by %p", __func__, lk, owner); /* * If we are holding also an interlock drop it * in order to avoid a deadlock if the lockmgr * owner is adaptively spinning on the * interlock itself. */ if (flags & LK_INTERLOCK) { class->lc_unlock(ilk); flags &= ~LK_INTERLOCK; } GIANT_SAVE(); while (LK_HOLDER(lk->lk_lock) == (uintptr_t)owner && TD_IS_RUNNING(owner)) cpu_spinwait(); GIANT_RESTORE(); continue; } else if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) != 0 && LK_SHARERS(x) && spintries < alk_retries) { if ((x & LK_EXCLUSIVE_SPINNERS) == 0 && !atomic_cmpset_ptr(&lk->lk_lock, x, x | LK_EXCLUSIVE_SPINNERS)) continue; if (flags & LK_INTERLOCK) { class->lc_unlock(ilk); flags &= ~LK_INTERLOCK; } GIANT_SAVE(); spintries++; for (i = 0; i < alk_loops; i++) { if (LOCK_LOG_TEST(&lk->lock_object, 0)) CTR4(KTR_LOCK, "%s: shared spinning on %p with %u and %u", __func__, lk, spintries, i); if ((lk->lk_lock & LK_EXCLUSIVE_SPINNERS) == 0) break; cpu_spinwait(); } GIANT_RESTORE(); if (i != alk_loops) continue; } #endif /* * Acquire the sleepqueue chain lock because we * probabilly will need to manipulate waiters flags. */ sleepq_lock(&lk->lock_object); x = lk->lk_lock; /* * if the lock has been released while we spun on * the sleepqueue chain lock just try again. */ if (x == LK_UNLOCKED) { sleepq_release(&lk->lock_object); continue; } #ifdef ADAPTIVE_LOCKMGRS /* * The current lock owner might have started executing * on another CPU (or the lock could have changed * owner) while we were waiting on the turnstile * chain lock. If so, drop the turnstile lock and try * again. */ if (LK_CAN_ADAPT(lk, flags) && (x & LK_SHARE) == 0 && LK_HOLDER(x) != LK_KERNPROC) { owner = (struct thread *)LK_HOLDER(x); if (TD_IS_RUNNING(owner)) { sleepq_release(&lk->lock_object); continue; } } #endif /* * The lock can be in the state where there is a * pending queue of waiters, but still no owner. * This happens when the lock is contested and an * owner is going to claim the lock. * If curthread is the one successfully acquiring it * claim lock ownership and return, preserving waiters * flags. */ v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); if ((x & ~v) == LK_UNLOCKED) { v &= ~LK_EXCLUSIVE_SPINNERS; if (atomic_cmpset_acq_ptr(&lk->lk_lock, x, tid | v)) { sleepq_release(&lk->lock_object); LOCK_LOG2(lk, "%s: %p claimed by a new writer", __func__, lk); break; } sleepq_release(&lk->lock_object); continue; } /* * Try to set the LK_EXCLUSIVE_WAITERS flag. If we * fail, loop back and retry. */ if ((x & LK_EXCLUSIVE_WAITERS) == 0) { if (!atomic_cmpset_ptr(&lk->lk_lock, x, x | LK_EXCLUSIVE_WAITERS)) { sleepq_release(&lk->lock_object); continue; } LOCK_LOG2(lk, "%s: %p set excl waiters flag", __func__, lk); } /* * As far as we have been unable to acquire the * exclusive lock and the exclusive waiters flag * is set, we will sleep. */ error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo, SQ_EXCLUSIVE_QUEUE); flags &= ~LK_INTERLOCK; if (error) { LOCK_LOG3(lk, "%s: interrupted sleep for %p with %d", __func__, lk, error); break; } LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", __func__, lk); } if (error == 0) { lock_profile_obtain_lock_success(&lk->lock_object, contested, waittime, file, line); LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line); WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file, line); TD_LOCKS_INC(curthread); STACK_SAVE(lk); } break; case LK_DOWNGRADE: _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line); LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line); WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line); TD_SLOCKS_INC(curthread); /* * In order to preserve waiters flags, just spin. */ for (;;) { x = lk->lk_lock; MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); x &= LK_ALL_WAITERS; if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x, LK_SHARERS_LOCK(1) | x)) break; cpu_spinwait(); } break; case LK_RELEASE: _lockmgr_assert(lk, KA_LOCKED, file, line); x = lk->lk_lock; if ((x & LK_SHARE) == 0) { /* * As first option, treact the lock as if it has not * any waiter. * Fix-up the tid var if the lock has been disowned. */ if (LK_HOLDER(x) == LK_KERNPROC) tid = LK_KERNPROC; else { WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); TD_LOCKS_DEC(curthread); } LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line); /* * The lock is held in exclusive mode. * If the lock is recursed also, then unrecurse it. */ if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) { LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk); lk->lk_recurse--; break; } if (tid != LK_KERNPROC) lock_profile_release_lock(&lk->lock_object); if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) break; sleepq_lock(&lk->lock_object); x = lk->lk_lock; v = LK_UNLOCKED; /* * If the lock has exclusive waiters, give them * preference in order to avoid deadlock with * shared runners up. * If interruptible sleeps left the exclusive queue * empty avoid a starvation for the threads sleeping * on the shared queue by giving them precedence * and cleaning up the exclusive waiters bit anyway. * Please note that lk_exslpfail count may be lying * about the real number of waiters with the * LK_SLEEPFAIL flag on because they may be used in * conjuction with interruptible sleeps so * lk_exslpfail might be considered an 'upper limit' * bound, including the edge cases. */ MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE); if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) { if (lk->lk_exslpfail < realexslp) { lk->lk_exslpfail = 0; queue = SQ_EXCLUSIVE_QUEUE; v |= (x & LK_SHARED_WAITERS); } else { lk->lk_exslpfail = 0; LOCK_LOG2(lk, "%s: %p has only LK_SLEEPFAIL sleepers", __func__, lk); LOCK_LOG2(lk, "%s: %p waking up threads on the exclusive queue", __func__, lk); wakeup_swapper = sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE); queue = SQ_SHARED_QUEUE; } } else { /* * Exclusive waiters sleeping with LK_SLEEPFAIL * on and using interruptible sleeps/timeout * may have left spourious lk_exslpfail counts * on, so clean it up anyway. */ lk->lk_exslpfail = 0; queue = SQ_SHARED_QUEUE; } LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue", __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : "exclusive"); atomic_store_rel_ptr(&lk->lk_lock, v); wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue); sleepq_release(&lk->lock_object); break; } else wakeup_swapper = wakeupshlk(lk, file, line); break; case LK_DRAIN: if (LK_CAN_WITNESS(flags)) WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, line, ilk); /* * Trying to drain a lock we already own will result in a * deadlock. */ if (lockmgr_xlocked(lk)) { if (flags & LK_INTERLOCK) class->lc_unlock(ilk); panic("%s: draining %s with the lock held @ %s:%d\n", __func__, iwmesg, file, line); } while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) { lock_profile_obtain_lock_failed(&lk->lock_object, &contested, &waittime); /* * If the lock is expected to not sleep just give up * and return. */ if (LK_TRYOP(flags)) { LOCK_LOG2(lk, "%s: %p fails the try operation", __func__, lk); error = EBUSY; break; } /* * Acquire the sleepqueue chain lock because we * probabilly will need to manipulate waiters flags. */ sleepq_lock(&lk->lock_object); x = lk->lk_lock; /* * if the lock has been released while we spun on * the sleepqueue chain lock just try again. */ if (x == LK_UNLOCKED) { sleepq_release(&lk->lock_object); continue; } v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); if ((x & ~v) == LK_UNLOCKED) { v = (x & ~LK_EXCLUSIVE_SPINNERS); /* * If interruptible sleeps left the exclusive * queue empty avoid a starvation for the * threads sleeping on the shared queue by * giving them precedence and cleaning up the * exclusive waiters bit anyway. * Please note that lk_exslpfail count may be * lying about the real number of waiters with * the LK_SLEEPFAIL flag on because they may * be used in conjuction with interruptible * sleeps so lk_exslpfail might be considered * an 'upper limit' bound, including the edge * cases. */ if (v & LK_EXCLUSIVE_WAITERS) { queue = SQ_EXCLUSIVE_QUEUE; v &= ~LK_EXCLUSIVE_WAITERS; } else { /* * Exclusive waiters sleeping with * LK_SLEEPFAIL on and using * interruptible sleeps/timeout may * have left spourious lk_exslpfail * counts on, so clean it up anyway. */ MPASS(v & LK_SHARED_WAITERS); lk->lk_exslpfail = 0; queue = SQ_SHARED_QUEUE; v &= ~LK_SHARED_WAITERS; } if (queue == SQ_EXCLUSIVE_QUEUE) { realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE); if (lk->lk_exslpfail >= realexslp) { lk->lk_exslpfail = 0; queue = SQ_SHARED_QUEUE; v &= ~LK_SHARED_WAITERS; if (realexslp != 0) { LOCK_LOG2(lk, "%s: %p has only LK_SLEEPFAIL sleepers", __func__, lk); LOCK_LOG2(lk, "%s: %p waking up threads on the exclusive queue", __func__, lk); wakeup_swapper = sleepq_broadcast( &lk->lock_object, SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE); } } else lk->lk_exslpfail = 0; } if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) { sleepq_release(&lk->lock_object); continue; } LOCK_LOG3(lk, "%s: %p waking up all threads on the %s queue", __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : "exclusive"); wakeup_swapper |= sleepq_broadcast( &lk->lock_object, SLEEPQ_LK, 0, queue); /* * If shared waiters have been woken up we need * to wait for one of them to acquire the lock * before to set the exclusive waiters in * order to avoid a deadlock. */ if (queue == SQ_SHARED_QUEUE) { for (v = lk->lk_lock; (v & LK_SHARE) && !LK_SHARERS(v); v = lk->lk_lock) cpu_spinwait(); } } /* * Try to set the LK_EXCLUSIVE_WAITERS flag. If we * fail, loop back and retry. */ if ((x & LK_EXCLUSIVE_WAITERS) == 0) { if (!atomic_cmpset_ptr(&lk->lk_lock, x, x | LK_EXCLUSIVE_WAITERS)) { sleepq_release(&lk->lock_object); continue; } LOCK_LOG2(lk, "%s: %p set drain waiters flag", __func__, lk); } /* * As far as we have been unable to acquire the * exclusive lock and the exclusive waiters flag * is set, we will sleep. */ if (flags & LK_INTERLOCK) { class->lc_unlock(ilk); flags &= ~LK_INTERLOCK; } GIANT_SAVE(); sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK, SQ_EXCLUSIVE_QUEUE); sleepq_wait(&lk->lock_object, ipri & PRIMASK); GIANT_RESTORE(); LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", __func__, lk); } if (error == 0) { lock_profile_obtain_lock_success(&lk->lock_object, contested, waittime, file, line); LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0, lk->lk_recurse, file, line); WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file, line); TD_LOCKS_INC(curthread); STACK_SAVE(lk); } break; default: if (flags & LK_INTERLOCK) class->lc_unlock(ilk); panic("%s: unknown lockmgr request 0x%x\n", __func__, op); } if (flags & LK_INTERLOCK) class->lc_unlock(ilk); if (wakeup_swapper) kick_proc0(); return (error); } void _lockmgr_disown(struct lock *lk, const char *file, int line) { uintptr_t tid, x; if (SCHEDULER_STOPPED()) return; tid = (uintptr_t)curthread; _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line); /* * If the owner is already LK_KERNPROC just skip the whole operation. */ if (LK_HOLDER(lk->lk_lock) != tid) return; lock_profile_release_lock(&lk->lock_object); LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line); WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); TD_LOCKS_DEC(curthread); STACK_SAVE(lk); /* * In order to preserve waiters flags, just spin. */ for (;;) { x = lk->lk_lock; MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); x &= LK_ALL_WAITERS; if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x, LK_KERNPROC | x)) return; cpu_spinwait(); } } void lockmgr_printinfo(const struct lock *lk) { struct thread *td; uintptr_t x; if (lk->lk_lock == LK_UNLOCKED) printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name); else if (lk->lk_lock & LK_SHARE) printf("lock type %s: SHARED (count %ju)\n", lk->lock_object.lo_name, (uintmax_t)LK_SHARERS(lk->lk_lock)); else { td = lockmgr_xholder(lk); printf("lock type %s: EXCL by thread %p " "(pid %d, %s, tid %d)\n", lk->lock_object.lo_name, td, td->td_proc->p_pid, td->td_proc->p_comm, td->td_tid); } x = lk->lk_lock; if (x & LK_EXCLUSIVE_WAITERS) printf(" with exclusive waiters pending\n"); if (x & LK_SHARED_WAITERS) printf(" with shared waiters pending\n"); if (x & LK_EXCLUSIVE_SPINNERS) printf(" with exclusive spinners pending\n"); STACK_PRINT(lk); } int lockstatus(const struct lock *lk) { uintptr_t v, x; int ret; ret = LK_SHARED; x = lk->lk_lock; v = LK_HOLDER(x); if ((x & LK_SHARE) == 0) { if (v == (uintptr_t)curthread || v == LK_KERNPROC) ret = LK_EXCLUSIVE; else ret = LK_EXCLOTHER; } else if (x == LK_UNLOCKED) ret = 0; return (ret); } #ifdef INVARIANT_SUPPORT FEATURE(invariant_support, "Support for modules compiled with INVARIANTS option"); #ifndef INVARIANTS #undef _lockmgr_assert #endif void _lockmgr_assert(const struct lock *lk, int what, const char *file, int line) { int slocked = 0; if (panicstr != NULL) return; switch (what) { case KA_SLOCKED: case KA_SLOCKED | KA_NOTRECURSED: case KA_SLOCKED | KA_RECURSED: slocked = 1; case KA_LOCKED: case KA_LOCKED | KA_NOTRECURSED: case KA_LOCKED | KA_RECURSED: #ifdef WITNESS /* * We cannot trust WITNESS if the lock is held in exclusive * mode and a call to lockmgr_disown() happened. * Workaround this skipping the check if the lock is held in * exclusive mode even for the KA_LOCKED case. */ if (slocked || (lk->lk_lock & LK_SHARE)) { witness_assert(&lk->lock_object, what, file, line); break; } #endif if (lk->lk_lock == LK_UNLOCKED || ((lk->lk_lock & LK_SHARE) == 0 && (slocked || (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))))) panic("Lock %s not %slocked @ %s:%d\n", lk->lock_object.lo_name, slocked ? "share" : "", file, line); if ((lk->lk_lock & LK_SHARE) == 0) { if (lockmgr_recursed(lk)) { if (what & KA_NOTRECURSED) panic("Lock %s recursed @ %s:%d\n", lk->lock_object.lo_name, file, line); } else if (what & KA_RECURSED) panic("Lock %s not recursed @ %s:%d\n", lk->lock_object.lo_name, file, line); } break; case KA_XLOCKED: case KA_XLOCKED | KA_NOTRECURSED: case KA_XLOCKED | KA_RECURSED: if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)) panic("Lock %s not exclusively locked @ %s:%d\n", lk->lock_object.lo_name, file, line); if (lockmgr_recursed(lk)) { if (what & KA_NOTRECURSED) panic("Lock %s recursed @ %s:%d\n", lk->lock_object.lo_name, file, line); } else if (what & KA_RECURSED) panic("Lock %s not recursed @ %s:%d\n", lk->lock_object.lo_name, file, line); break; case KA_UNLOCKED: if (lockmgr_xlocked(lk) || lockmgr_disowned(lk)) panic("Lock %s exclusively locked @ %s:%d\n", lk->lock_object.lo_name, file, line); break; default: panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file, line); } } #endif #ifdef DDB int lockmgr_chain(struct thread *td, struct thread **ownerp) { struct lock *lk; lk = td->td_wchan; if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr) return (0); db_printf("blocked on lockmgr %s", lk->lock_object.lo_name); if (lk->lk_lock & LK_SHARE) db_printf("SHARED (count %ju)\n", (uintmax_t)LK_SHARERS(lk->lk_lock)); else db_printf("EXCL\n"); *ownerp = lockmgr_xholder(lk); return (1); } static void db_show_lockmgr(const struct lock_object *lock) { struct thread *td; const struct lock *lk; lk = (const struct lock *)lock; db_printf(" state: "); if (lk->lk_lock == LK_UNLOCKED) db_printf("UNLOCKED\n"); else if (lk->lk_lock & LK_SHARE) db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock)); else { td = lockmgr_xholder(lk); if (td == (struct thread *)LK_KERNPROC) db_printf("XLOCK: LK_KERNPROC\n"); else db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); if (lockmgr_recursed(lk)) db_printf(" recursed: %d\n", lk->lk_recurse); } db_printf(" waiters: "); switch (lk->lk_lock & LK_ALL_WAITERS) { case LK_SHARED_WAITERS: db_printf("shared\n"); break; case LK_EXCLUSIVE_WAITERS: db_printf("exclusive\n"); break; case LK_ALL_WAITERS: db_printf("shared and exclusive\n"); break; default: db_printf("none\n"); } db_printf(" spinners: "); if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS) db_printf("exclusive\n"); else db_printf("none\n"); } #endif