/*- * SPDX-License-Identifier: BSD-3-Clause * * Copyright (c) 1998 Berkeley Software Design, Inc. 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, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Berkeley Software Design Inc's name may not be used to endorse or * promote products derived from this software without specific prior * written permission. * * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``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 BERKELEY SOFTWARE DESIGN INC 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. * * from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $ * and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $ */ /* * Implementation of turnstiles used to hold queue of threads blocked on * non-sleepable locks. Sleepable locks use condition variables to * implement their queues. Turnstiles differ from a sleep queue in that * turnstile queue's are assigned to a lock held by an owning thread. Thus, * when one thread is enqueued onto a turnstile, it can lend its priority * to the owning thread. * * We wish to avoid bloating locks with an embedded turnstile and we do not * want to use back-pointers in the locks for the same reason. Thus, we * use a similar approach to that of Solaris 7 as described in Solaris * Internals by Jim Mauro and Richard McDougall. Turnstiles are looked up * in a hash table based on the address of the lock. Each entry in the * hash table is a linked-lists of turnstiles and is called a turnstile * chain. Each chain contains a spin mutex that protects all of the * turnstiles in the chain. * * Each time a thread is created, a turnstile is allocated from a UMA zone * and attached to that thread. When a thread blocks on a lock, if it is the * first thread to block, it lends its turnstile to the lock. If the lock * already has a turnstile, then it gives its turnstile to the lock's * turnstile's free list. When a thread is woken up, it takes a turnstile from * the free list if there are any other waiters. If it is the only thread * blocked on the lock, then it reclaims the turnstile associated with the lock * and removes it from the hash table. */ #include __FBSDID("$FreeBSD$"); #include "opt_ddb.h" #include "opt_turnstile_profiling.h" #include "opt_sched.h" #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef DDB #include #include #include #endif /* * Constants for the hash table of turnstile chains. TC_SHIFT is a magic * number chosen because the sleep queue's use the same value for the * shift. Basically, we ignore the lower 8 bits of the address. * TC_TABLESIZE must be a power of two for TC_MASK to work properly. */ #define TC_TABLESIZE 128 /* Must be power of 2. */ #define TC_MASK (TC_TABLESIZE - 1) #define TC_SHIFT 8 #define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK) #define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)] /* * There are three different lists of turnstiles as follows. The list * connected by ts_link entries is a per-thread list of all the turnstiles * attached to locks that we own. This is used to fixup our priority when * a lock is released. The other two lists use the ts_hash entries. The * first of these two is the turnstile chain list that a turnstile is on * when it is attached to a lock. The second list to use ts_hash is the * free list hung off of a turnstile that is attached to a lock. * * Each turnstile contains three lists of threads. The two ts_blocked lists * are linked list of threads blocked on the turnstile's lock. One list is * for exclusive waiters, and the other is for shared waiters. The * ts_pending list is a linked list of threads previously awakened by * turnstile_signal() or turnstile_wait() that are waiting to be put on * the run queue. * * Locking key: * c - turnstile chain lock * q - td_contested lock */ struct turnstile { struct mtx ts_lock; /* Spin lock for self. */ struct threadqueue ts_blocked[2]; /* (c + q) Blocked threads. */ struct threadqueue ts_pending; /* (c) Pending threads. */ LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */ LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */ LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */ struct lock_object *ts_lockobj; /* (c) Lock we reference. */ struct thread *ts_owner; /* (c + q) Who owns the lock. */ }; struct turnstile_chain { LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */ struct mtx tc_lock; /* Spin lock for this chain. */ #ifdef TURNSTILE_PROFILING u_int tc_depth; /* Length of tc_queues. */ u_int tc_max_depth; /* Max length of tc_queues. */ #endif }; #ifdef TURNSTILE_PROFILING u_int turnstile_max_depth; static SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "turnstile profiling"); static SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "turnstile chain stats"); SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD, &turnstile_max_depth, 0, "maximum depth achieved of a single chain"); #endif static struct mtx td_contested_lock; static struct turnstile_chain turnstile_chains[TC_TABLESIZE]; static uma_zone_t turnstile_zone; /* * Prototypes for non-exported routines. */ static void init_turnstile0(void *dummy); #ifdef TURNSTILE_PROFILING static void init_turnstile_profiling(void *arg); #endif static void propagate_priority(struct thread *td); static int turnstile_adjust_thread(struct turnstile *ts, struct thread *td); static struct thread *turnstile_first_waiter(struct turnstile *ts); static void turnstile_setowner(struct turnstile *ts, struct thread *owner); #ifdef INVARIANTS static void turnstile_dtor(void *mem, int size, void *arg); #endif static int turnstile_init(void *mem, int size, int flags); static void turnstile_fini(void *mem, int size); SDT_PROVIDER_DECLARE(sched); SDT_PROBE_DEFINE(sched, , , sleep); SDT_PROBE_DEFINE2(sched, , , wakeup, "struct thread *", "struct proc *"); static inline void propagate_unlock_ts(struct turnstile *top, struct turnstile *ts) { if (ts != top) mtx_unlock_spin(&ts->ts_lock); } static inline void propagate_unlock_td(struct turnstile *top, struct thread *td) { if (td->td_lock != &top->ts_lock) thread_unlock(td); } /* * Walks the chain of turnstiles and their owners to propagate the priority * of the thread being blocked to all the threads holding locks that have to * release their locks before this thread can run again. */ static void propagate_priority(struct thread *td) { struct turnstile *ts, *top; int pri; THREAD_LOCK_ASSERT(td, MA_OWNED); pri = td->td_priority; top = ts = td->td_blocked; THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); /* * The original turnstile lock is held across the entire * operation. We only ever lock down the chain so the lock * order is constant. */ for (;;) { td = ts->ts_owner; if (td == NULL) { /* * This might be a read lock with no owner. There's * not much we can do, so just bail. */ propagate_unlock_ts(top, ts); return; } /* * Wait for the thread lock to be stable and then only * acquire if it is not the turnstile lock. */ thread_lock_block_wait(td); if (td->td_lock != &ts->ts_lock) { thread_lock_flags(td, MTX_DUPOK); propagate_unlock_ts(top, ts); } MPASS(td->td_proc != NULL); MPASS(td->td_proc->p_magic == P_MAGIC); /* * If the thread is asleep, then we are probably about * to deadlock. To make debugging this easier, show * backtrace of misbehaving thread and panic to not * leave the kernel deadlocked. */ if (TD_IS_SLEEPING(td)) { printf( "Sleeping thread (tid %d, pid %d) owns a non-sleepable lock\n", td->td_tid, td->td_proc->p_pid); kdb_backtrace_thread(td); panic("sleeping thread"); } /* * If this thread already has higher priority than the * thread that is being blocked, we are finished. */ if (td->td_priority <= pri) { propagate_unlock_td(top, td); return; } /* * Bump this thread's priority. */ sched_lend_prio(td, pri); /* * If lock holder is actually running or on the run queue * then we are done. */ if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) { MPASS(td->td_blocked == NULL); propagate_unlock_td(top, td); return; } #ifndef SMP /* * For UP, we check to see if td is curthread (this shouldn't * ever happen however as it would mean we are in a deadlock.) */ KASSERT(td != curthread, ("Deadlock detected")); #endif /* * If we aren't blocked on a lock, we should be. */ KASSERT(TD_ON_LOCK(td), ( "thread %d(%s):%d holds %s but isn't blocked on a lock\n", td->td_tid, td->td_name, TD_GET_STATE(td), ts->ts_lockobj->lo_name)); /* * Pick up the lock that td is blocked on. */ ts = td->td_blocked; MPASS(ts != NULL); THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); /* Resort td on the list if needed. */ if (!turnstile_adjust_thread(ts, td)) { propagate_unlock_ts(top, ts); return; } /* The thread lock is released as ts lock above. */ } } /* * Adjust the thread's position on a turnstile after its priority has been * changed. */ static int turnstile_adjust_thread(struct turnstile *ts, struct thread *td) { struct thread *td1, *td2; int queue; THREAD_LOCK_ASSERT(td, MA_OWNED); MPASS(TD_ON_LOCK(td)); /* * This thread may not be blocked on this turnstile anymore * but instead might already be woken up on another CPU * that is waiting on the thread lock in turnstile_unpend() to * finish waking this thread up. We can detect this case * by checking to see if this thread has been given a * turnstile by either turnstile_signal() or * turnstile_broadcast(). In this case, treat the thread as * if it was already running. */ if (td->td_turnstile != NULL) return (0); /* * Check if the thread needs to be moved on the blocked chain. * It needs to be moved if either its priority is lower than * the previous thread or higher than the next thread. */ THREAD_LOCKPTR_BLOCKED_ASSERT(td, &ts->ts_lock); td1 = TAILQ_PREV(td, threadqueue, td_lockq); td2 = TAILQ_NEXT(td, td_lockq); if ((td1 != NULL && td->td_priority < td1->td_priority) || (td2 != NULL && td->td_priority > td2->td_priority)) { /* * Remove thread from blocked chain and determine where * it should be moved to. */ queue = td->td_tsqueue; MPASS(queue == TS_EXCLUSIVE_QUEUE || queue == TS_SHARED_QUEUE); mtx_lock_spin(&td_contested_lock); TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq); TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) { MPASS(td1->td_proc->p_magic == P_MAGIC); if (td1->td_priority > td->td_priority) break; } if (td1 == NULL) TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); else TAILQ_INSERT_BEFORE(td1, td, td_lockq); mtx_unlock_spin(&td_contested_lock); if (td1 == NULL) CTR3(KTR_LOCK, "turnstile_adjust_thread: td %d put at tail on [%p] %s", td->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name); else CTR4(KTR_LOCK, "turnstile_adjust_thread: td %d moved before %d on [%p] %s", td->td_tid, td1->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name); } return (1); } /* * Early initialization of turnstiles. This is not done via a SYSINIT() * since this needs to be initialized very early when mutexes are first * initialized. */ void init_turnstiles(void) { int i; for (i = 0; i < TC_TABLESIZE; i++) { LIST_INIT(&turnstile_chains[i].tc_turnstiles); mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain", NULL, MTX_SPIN); } mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN); LIST_INIT(&thread0.td_contested); thread0.td_turnstile = NULL; } #ifdef TURNSTILE_PROFILING static void init_turnstile_profiling(void *arg) { struct sysctl_oid *chain_oid; char chain_name[10]; int i; for (i = 0; i < TC_TABLESIZE; i++) { snprintf(chain_name, sizeof(chain_name), "%d", i); chain_oid = SYSCTL_ADD_NODE(NULL, SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO, chain_name, CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, "turnstile chain stats"); SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO, "depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0, NULL); SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO, "max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth, 0, NULL); } } SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile_profiling, NULL); #endif static void init_turnstile0(void *dummy) { turnstile_zone = uma_zcreate("TURNSTILE", sizeof(struct turnstile), NULL, #ifdef INVARIANTS turnstile_dtor, #else NULL, #endif turnstile_init, turnstile_fini, UMA_ALIGN_CACHE, UMA_ZONE_NOFREE); thread0.td_turnstile = turnstile_alloc(); } SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL); /* * Update a thread on the turnstile list after it's priority has been changed. * The old priority is passed in as an argument. */ void turnstile_adjust(struct thread *td, u_char oldpri) { struct turnstile *ts; MPASS(TD_ON_LOCK(td)); /* * Pick up the lock that td is blocked on. */ ts = td->td_blocked; MPASS(ts != NULL); THREAD_LOCKPTR_BLOCKED_ASSERT(td, &ts->ts_lock); mtx_assert(&ts->ts_lock, MA_OWNED); /* Resort the turnstile on the list. */ if (!turnstile_adjust_thread(ts, td)) return; /* * If our priority was lowered and we are at the head of the * turnstile, then propagate our new priority up the chain. * Note that we currently don't try to revoke lent priorities * when our priority goes up. */ MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE || td->td_tsqueue == TS_SHARED_QUEUE); if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) && td->td_priority < oldpri) { propagate_priority(td); } } /* * Set the owner of the lock this turnstile is attached to. */ static void turnstile_setowner(struct turnstile *ts, struct thread *owner) { mtx_assert(&td_contested_lock, MA_OWNED); MPASS(ts->ts_owner == NULL); /* A shared lock might not have an owner. */ if (owner == NULL) return; MPASS(owner->td_proc->p_magic == P_MAGIC); ts->ts_owner = owner; LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link); } #ifdef INVARIANTS /* * UMA zone item deallocator. */ static void turnstile_dtor(void *mem, int size, void *arg) { struct turnstile *ts; ts = mem; MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE])); MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])); MPASS(TAILQ_EMPTY(&ts->ts_pending)); } #endif /* * UMA zone item initializer. */ static int turnstile_init(void *mem, int size, int flags) { struct turnstile *ts; bzero(mem, size); ts = mem; TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]); TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]); TAILQ_INIT(&ts->ts_pending); LIST_INIT(&ts->ts_free); mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN); return (0); } static void turnstile_fini(void *mem, int size) { struct turnstile *ts; ts = mem; mtx_destroy(&ts->ts_lock); } /* * Get a turnstile for a new thread. */ struct turnstile * turnstile_alloc(void) { return (uma_zalloc(turnstile_zone, M_WAITOK)); } /* * Free a turnstile when a thread is destroyed. */ void turnstile_free(struct turnstile *ts) { uma_zfree(turnstile_zone, ts); } /* * Lock the turnstile chain associated with the specified lock. */ void turnstile_chain_lock(struct lock_object *lock) { struct turnstile_chain *tc; tc = TC_LOOKUP(lock); mtx_lock_spin(&tc->tc_lock); } struct turnstile * turnstile_trywait(struct lock_object *lock) { struct turnstile_chain *tc; struct turnstile *ts; tc = TC_LOOKUP(lock); mtx_lock_spin(&tc->tc_lock); LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) if (ts->ts_lockobj == lock) { mtx_lock_spin(&ts->ts_lock); return (ts); } ts = curthread->td_turnstile; MPASS(ts != NULL); mtx_lock_spin(&ts->ts_lock); KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer")); ts->ts_lockobj = lock; return (ts); } bool turnstile_lock(struct turnstile *ts, struct lock_object **lockp, struct thread **tdp) { struct turnstile_chain *tc; struct lock_object *lock; if ((lock = ts->ts_lockobj) == NULL) return (false); tc = TC_LOOKUP(lock); mtx_lock_spin(&tc->tc_lock); mtx_lock_spin(&ts->ts_lock); if (__predict_false(lock != ts->ts_lockobj)) { mtx_unlock_spin(&tc->tc_lock); mtx_unlock_spin(&ts->ts_lock); return (false); } *lockp = lock; *tdp = ts->ts_owner; return (true); } void turnstile_unlock(struct turnstile *ts, struct lock_object *lock) { struct turnstile_chain *tc; mtx_assert(&ts->ts_lock, MA_OWNED); mtx_unlock_spin(&ts->ts_lock); if (ts == curthread->td_turnstile) ts->ts_lockobj = NULL; tc = TC_LOOKUP(lock); mtx_unlock_spin(&tc->tc_lock); } void turnstile_assert(struct turnstile *ts) { MPASS(ts->ts_lockobj == NULL); } void turnstile_cancel(struct turnstile *ts) { struct turnstile_chain *tc; struct lock_object *lock; mtx_assert(&ts->ts_lock, MA_OWNED); mtx_unlock_spin(&ts->ts_lock); lock = ts->ts_lockobj; if (ts == curthread->td_turnstile) ts->ts_lockobj = NULL; tc = TC_LOOKUP(lock); mtx_unlock_spin(&tc->tc_lock); } /* * Look up the turnstile for a lock in the hash table locking the associated * turnstile chain along the way. If no turnstile is found in the hash * table, NULL is returned. */ struct turnstile * turnstile_lookup(struct lock_object *lock) { struct turnstile_chain *tc; struct turnstile *ts; tc = TC_LOOKUP(lock); mtx_assert(&tc->tc_lock, MA_OWNED); LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) if (ts->ts_lockobj == lock) { mtx_lock_spin(&ts->ts_lock); return (ts); } return (NULL); } /* * Unlock the turnstile chain associated with a given lock. */ void turnstile_chain_unlock(struct lock_object *lock) { struct turnstile_chain *tc; tc = TC_LOOKUP(lock); mtx_unlock_spin(&tc->tc_lock); } /* * Return a pointer to the thread waiting on this turnstile with the * most important priority or NULL if the turnstile has no waiters. */ static struct thread * turnstile_first_waiter(struct turnstile *ts) { struct thread *std, *xtd; std = TAILQ_FIRST(&ts->ts_blocked[TS_SHARED_QUEUE]); xtd = TAILQ_FIRST(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]); if (xtd == NULL || (std != NULL && std->td_priority < xtd->td_priority)) return (std); return (xtd); } /* * Take ownership of a turnstile and adjust the priority of the new * owner appropriately. */ void turnstile_claim(struct turnstile *ts) { struct thread *td, *owner; struct turnstile_chain *tc; mtx_assert(&ts->ts_lock, MA_OWNED); MPASS(ts != curthread->td_turnstile); owner = curthread; mtx_lock_spin(&td_contested_lock); turnstile_setowner(ts, owner); mtx_unlock_spin(&td_contested_lock); td = turnstile_first_waiter(ts); MPASS(td != NULL); MPASS(td->td_proc->p_magic == P_MAGIC); THREAD_LOCKPTR_BLOCKED_ASSERT(td, &ts->ts_lock); /* * Update the priority of the new owner if needed. */ thread_lock(owner); if (td->td_priority < owner->td_priority) sched_lend_prio(owner, td->td_priority); thread_unlock(owner); tc = TC_LOOKUP(ts->ts_lockobj); mtx_unlock_spin(&ts->ts_lock); mtx_unlock_spin(&tc->tc_lock); } /* * Block the current thread on the turnstile assicated with 'lock'. This * function will context switch and not return until this thread has been * woken back up. This function must be called with the appropriate * turnstile chain locked and will return with it unlocked. */ void turnstile_wait(struct turnstile *ts, struct thread *owner, int queue) { struct turnstile_chain *tc; struct thread *td, *td1; struct lock_object *lock; td = curthread; mtx_assert(&ts->ts_lock, MA_OWNED); if (owner) MPASS(owner->td_proc->p_magic == P_MAGIC); MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); /* * If the lock does not already have a turnstile, use this thread's * turnstile. Otherwise insert the current thread into the * turnstile already in use by this lock. */ tc = TC_LOOKUP(ts->ts_lockobj); mtx_assert(&tc->tc_lock, MA_OWNED); if (ts == td->td_turnstile) { #ifdef TURNSTILE_PROFILING tc->tc_depth++; if (tc->tc_depth > tc->tc_max_depth) { tc->tc_max_depth = tc->tc_depth; if (tc->tc_max_depth > turnstile_max_depth) turnstile_max_depth = tc->tc_max_depth; } #endif LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash); KASSERT(TAILQ_EMPTY(&ts->ts_pending), ("thread's turnstile has pending threads")); KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]), ("thread's turnstile has exclusive waiters")); KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]), ("thread's turnstile has shared waiters")); KASSERT(LIST_EMPTY(&ts->ts_free), ("thread's turnstile has a non-empty free list")); MPASS(ts->ts_lockobj != NULL); mtx_lock_spin(&td_contested_lock); TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); turnstile_setowner(ts, owner); mtx_unlock_spin(&td_contested_lock); } else { TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) if (td1->td_priority > td->td_priority) break; mtx_lock_spin(&td_contested_lock); if (td1 != NULL) TAILQ_INSERT_BEFORE(td1, td, td_lockq); else TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); MPASS(owner == ts->ts_owner); mtx_unlock_spin(&td_contested_lock); MPASS(td->td_turnstile != NULL); LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash); } thread_lock(td); thread_lock_set(td, &ts->ts_lock); td->td_turnstile = NULL; /* Save who we are blocked on and switch. */ lock = ts->ts_lockobj; td->td_tsqueue = queue; td->td_blocked = ts; td->td_lockname = lock->lo_name; td->td_blktick = ticks; TD_SET_LOCK(td); mtx_unlock_spin(&tc->tc_lock); propagate_priority(td); if (LOCK_LOG_TEST(lock, 0)) CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__, td->td_tid, lock, lock->lo_name); SDT_PROBE0(sched, , , sleep); THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); mi_switch(SW_VOL | SWT_TURNSTILE); if (LOCK_LOG_TEST(lock, 0)) CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s", __func__, td->td_tid, lock, lock->lo_name); } /* * Pick the highest priority thread on this turnstile and put it on the * pending list. This must be called with the turnstile chain locked. */ int turnstile_signal(struct turnstile *ts, int queue) { struct turnstile_chain *tc __unused; struct thread *td; int empty; MPASS(ts != NULL); mtx_assert(&ts->ts_lock, MA_OWNED); MPASS(curthread->td_proc->p_magic == P_MAGIC); MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL); MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); /* * Pick the highest priority thread blocked on this lock and * move it to the pending list. */ td = TAILQ_FIRST(&ts->ts_blocked[queue]); MPASS(td->td_proc->p_magic == P_MAGIC); mtx_lock_spin(&td_contested_lock); TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq); mtx_unlock_spin(&td_contested_lock); TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq); /* * If the turnstile is now empty, remove it from its chain and * give it to the about-to-be-woken thread. Otherwise take a * turnstile from the free list and give it to the thread. */ empty = TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) && TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]); if (empty) { tc = TC_LOOKUP(ts->ts_lockobj); mtx_assert(&tc->tc_lock, MA_OWNED); MPASS(LIST_EMPTY(&ts->ts_free)); #ifdef TURNSTILE_PROFILING tc->tc_depth--; #endif } else ts = LIST_FIRST(&ts->ts_free); MPASS(ts != NULL); LIST_REMOVE(ts, ts_hash); td->td_turnstile = ts; return (empty); } /* * Put all blocked threads on the pending list. This must be called with * the turnstile chain locked. */ void turnstile_broadcast(struct turnstile *ts, int queue) { struct turnstile_chain *tc __unused; struct turnstile *ts1; struct thread *td; MPASS(ts != NULL); mtx_assert(&ts->ts_lock, MA_OWNED); MPASS(curthread->td_proc->p_magic == P_MAGIC); MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL); /* * We must have the chain locked so that we can remove the empty * turnstile from the hash queue. */ tc = TC_LOOKUP(ts->ts_lockobj); mtx_assert(&tc->tc_lock, MA_OWNED); MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); /* * Transfer the blocked list to the pending list. */ mtx_lock_spin(&td_contested_lock); TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked[queue], td_lockq); mtx_unlock_spin(&td_contested_lock); /* * Give a turnstile to each thread. The last thread gets * this turnstile if the turnstile is empty. */ TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) { if (LIST_EMPTY(&ts->ts_free)) { MPASS(TAILQ_NEXT(td, td_lockq) == NULL); ts1 = ts; #ifdef TURNSTILE_PROFILING tc->tc_depth--; #endif } else ts1 = LIST_FIRST(&ts->ts_free); MPASS(ts1 != NULL); LIST_REMOVE(ts1, ts_hash); td->td_turnstile = ts1; } } static u_char turnstile_calc_unlend_prio_locked(struct thread *td) { struct turnstile *nts; u_char cp, pri; THREAD_LOCK_ASSERT(td, MA_OWNED); mtx_assert(&td_contested_lock, MA_OWNED); pri = PRI_MAX; LIST_FOREACH(nts, &td->td_contested, ts_link) { cp = turnstile_first_waiter(nts)->td_priority; if (cp < pri) pri = cp; } return (pri); } /* * Wakeup all threads on the pending list and adjust the priority of the * current thread appropriately. This must be called with the turnstile * chain locked. */ void turnstile_unpend(struct turnstile *ts) { TAILQ_HEAD( ,thread) pending_threads; struct thread *td; u_char pri; MPASS(ts != NULL); mtx_assert(&ts->ts_lock, MA_OWNED); MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL); MPASS(!TAILQ_EMPTY(&ts->ts_pending)); /* * Move the list of pending threads out of the turnstile and * into a local variable. */ TAILQ_INIT(&pending_threads); TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq); #ifdef INVARIANTS if (TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) && TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])) ts->ts_lockobj = NULL; #endif /* * Adjust the priority of curthread based on other contested * locks it owns. Don't lower the priority below the base * priority however. */ td = curthread; thread_lock(td); mtx_lock_spin(&td_contested_lock); /* * Remove the turnstile from this thread's list of contested locks * since this thread doesn't own it anymore. New threads will * not be blocking on the turnstile until it is claimed by a new * owner. There might not be a current owner if this is a shared * lock. */ if (ts->ts_owner != NULL) { ts->ts_owner = NULL; LIST_REMOVE(ts, ts_link); } pri = turnstile_calc_unlend_prio_locked(td); mtx_unlock_spin(&td_contested_lock); sched_unlend_prio(td, pri); thread_unlock(td); /* * Wake up all the pending threads. If a thread is not blocked * on a lock, then it is currently executing on another CPU in * turnstile_wait() or sitting on a run queue waiting to resume * in turnstile_wait(). Set a flag to force it to try to acquire * the lock again instead of blocking. */ while (!TAILQ_EMPTY(&pending_threads)) { td = TAILQ_FIRST(&pending_threads); TAILQ_REMOVE(&pending_threads, td, td_lockq); SDT_PROBE2(sched, , , wakeup, td, td->td_proc); thread_lock_block_wait(td); THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); MPASS(td->td_proc->p_magic == P_MAGIC); MPASS(TD_ON_LOCK(td)); TD_CLR_LOCK(td); MPASS(TD_CAN_RUN(td)); td->td_blocked = NULL; td->td_lockname = NULL; td->td_blktick = 0; #ifdef INVARIANTS td->td_tsqueue = 0xff; #endif sched_add(td, SRQ_HOLD | SRQ_BORING); } mtx_unlock_spin(&ts->ts_lock); } /* * Give up ownership of a turnstile. This must be called with the * turnstile chain locked. */ void turnstile_disown(struct turnstile *ts) { struct thread *td; u_char pri; MPASS(ts != NULL); mtx_assert(&ts->ts_lock, MA_OWNED); MPASS(ts->ts_owner == curthread); MPASS(TAILQ_EMPTY(&ts->ts_pending)); MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) || !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])); /* * Remove the turnstile from this thread's list of contested locks * since this thread doesn't own it anymore. New threads will * not be blocking on the turnstile until it is claimed by a new * owner. */ mtx_lock_spin(&td_contested_lock); ts->ts_owner = NULL; LIST_REMOVE(ts, ts_link); mtx_unlock_spin(&td_contested_lock); /* * Adjust the priority of curthread based on other contested * locks it owns. Don't lower the priority below the base * priority however. */ td = curthread; thread_lock(td); mtx_unlock_spin(&ts->ts_lock); mtx_lock_spin(&td_contested_lock); pri = turnstile_calc_unlend_prio_locked(td); mtx_unlock_spin(&td_contested_lock); sched_unlend_prio(td, pri); thread_unlock(td); } /* * Return the first thread in a turnstile. */ struct thread * turnstile_head(struct turnstile *ts, int queue) { #ifdef INVARIANTS MPASS(ts != NULL); MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); mtx_assert(&ts->ts_lock, MA_OWNED); #endif return (TAILQ_FIRST(&ts->ts_blocked[queue])); } /* * Returns true if a sub-queue of a turnstile is empty. */ int turnstile_empty(struct turnstile *ts, int queue) { #ifdef INVARIANTS MPASS(ts != NULL); MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); mtx_assert(&ts->ts_lock, MA_OWNED); #endif return (TAILQ_EMPTY(&ts->ts_blocked[queue])); } #ifdef DDB static void print_thread(struct thread *td, const char *prefix) { db_printf("%s%p (tid %d, pid %d, \"%s\")\n", prefix, td, td->td_tid, td->td_proc->p_pid, td->td_name); } static void print_queue(struct threadqueue *queue, const char *header, const char *prefix) { struct thread *td; db_printf("%s:\n", header); if (TAILQ_EMPTY(queue)) { db_printf("%sempty\n", prefix); return; } TAILQ_FOREACH(td, queue, td_lockq) { print_thread(td, prefix); } } DB_SHOW_COMMAND(turnstile, db_show_turnstile) { struct turnstile_chain *tc; struct turnstile *ts; struct lock_object *lock; int i; if (!have_addr) return; /* * First, see if there is an active turnstile for the lock indicated * by the address. */ lock = (struct lock_object *)addr; tc = TC_LOOKUP(lock); LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) if (ts->ts_lockobj == lock) goto found; /* * Second, see if there is an active turnstile at the address * indicated. */ for (i = 0; i < TC_TABLESIZE; i++) LIST_FOREACH(ts, &turnstile_chains[i].tc_turnstiles, ts_hash) { if (ts == (struct turnstile *)addr) goto found; } db_printf("Unable to locate a turnstile via %p\n", (void *)addr); return; found: lock = ts->ts_lockobj; db_printf("Lock: %p - (%s) %s\n", lock, LOCK_CLASS(lock)->lc_name, lock->lo_name); if (ts->ts_owner) print_thread(ts->ts_owner, "Lock Owner: "); else db_printf("Lock Owner: none\n"); print_queue(&ts->ts_blocked[TS_SHARED_QUEUE], "Shared Waiters", "\t"); print_queue(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE], "Exclusive Waiters", "\t"); print_queue(&ts->ts_pending, "Pending Threads", "\t"); } /* * Show all the threads a particular thread is waiting on based on * non-spin locks. */ static void print_lockchain(struct thread *td, const char *prefix) { struct lock_object *lock; struct lock_class *class; struct turnstile *ts; struct thread *owner; /* * Follow the chain. We keep walking as long as the thread is * blocked on a lock that has an owner. */ while (!db_pager_quit) { if (td == (void *)LK_KERNPROC) { db_printf("%sdisowned (LK_KERNPROC)\n", prefix); return; } db_printf("%sthread %d (pid %d, %s) is ", prefix, td->td_tid, td->td_proc->p_pid, td->td_name); switch (TD_GET_STATE(td)) { case TDS_INACTIVE: db_printf("inactive\n"); return; case TDS_CAN_RUN: db_printf("runnable\n"); return; case TDS_RUNQ: db_printf("on a run queue\n"); return; case TDS_RUNNING: db_printf("running on CPU %d\n", td->td_oncpu); return; case TDS_INHIBITED: if (TD_ON_LOCK(td)) { ts = td->td_blocked; lock = ts->ts_lockobj; class = LOCK_CLASS(lock); db_printf("blocked on lock %p (%s) \"%s\"\n", lock, class->lc_name, lock->lo_name); if (ts->ts_owner == NULL) return; td = ts->ts_owner; break; } else if (TD_ON_SLEEPQ(td)) { if (!lockmgr_chain(td, &owner) && !sx_chain(td, &owner)) { db_printf("sleeping on %p \"%s\"\n", td->td_wchan, td->td_wmesg); return; } if (owner == NULL) return; td = owner; break; } db_printf("inhibited: %s\n", KTDSTATE(td)); return; default: db_printf("??? (%#x)\n", TD_GET_STATE(td)); return; } } } DB_SHOW_COMMAND(lockchain, db_show_lockchain) { struct thread *td; /* Figure out which thread to start with. */ if (have_addr) td = db_lookup_thread(addr, true); else td = kdb_thread; print_lockchain(td, ""); } DB_SHOW_ALIAS(sleepchain, db_show_lockchain); DB_SHOW_ALL_COMMAND(chains, db_show_allchains) { struct thread *td; struct proc *p; int i; i = 1; FOREACH_PROC_IN_SYSTEM(p) { FOREACH_THREAD_IN_PROC(p, td) { if ((TD_ON_LOCK(td) && LIST_EMPTY(&td->td_contested)) || (TD_IS_INHIBITED(td) && TD_ON_SLEEPQ(td))) { db_printf("chain %d:\n", i++); print_lockchain(td, " "); } if (db_pager_quit) return; } } } DB_SHOW_ALIAS_FLAGS(allchains, db_show_allchains, DB_CMD_MEMSAFE); static void print_waiters(struct turnstile *ts, int indent); static void print_waiter(struct thread *td, int indent) { struct turnstile *ts; int i; if (db_pager_quit) return; for (i = 0; i < indent; i++) db_printf(" "); print_thread(td, "thread "); LIST_FOREACH(ts, &td->td_contested, ts_link) print_waiters(ts, indent + 1); } static void print_waiters(struct turnstile *ts, int indent) { struct lock_object *lock; struct lock_class *class; struct thread *td; int i; if (db_pager_quit) return; lock = ts->ts_lockobj; class = LOCK_CLASS(lock); for (i = 0; i < indent; i++) db_printf(" "); db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, lock->lo_name); TAILQ_FOREACH(td, &ts->ts_blocked[TS_EXCLUSIVE_QUEUE], td_lockq) print_waiter(td, indent + 1); TAILQ_FOREACH(td, &ts->ts_blocked[TS_SHARED_QUEUE], td_lockq) print_waiter(td, indent + 1); TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) print_waiter(td, indent + 1); } DB_SHOW_COMMAND(locktree, db_show_locktree) { struct lock_object *lock; struct lock_class *class; struct turnstile_chain *tc; struct turnstile *ts; if (!have_addr) return; lock = (struct lock_object *)addr; tc = TC_LOOKUP(lock); LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) if (ts->ts_lockobj == lock) break; if (ts == NULL) { class = LOCK_CLASS(lock); db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, lock->lo_name); } else print_waiters(ts, 0); } #endif