diff --git a/sys/kern/kern_rangelock.c b/sys/kern/kern_rangelock.c index 89b52d2550f0..20b65778c06d 100644 --- a/sys/kern/kern_rangelock.c +++ b/sys/kern/kern_rangelock.c @@ -1,729 +1,731 @@ /*- * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) 2009 Konstantin Belousov * Copyright (c) 2023 The FreeBSD Foundation * * Portions of this software were developed by * Konstantin Belousov under sponsorship from * the FreeBSD Foundation. * * 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 unmodified, 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. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 #include #include #include #include #include #include #include #include #include #include /* * Immediately after initialization (subject to 'rangelock_cheat' * below), and until a request comes that conflicts with granted ones * based on type, rangelocks serve requests in the "cheating" mode. * In this mode, a rangelock behaves like a sxlock, as if each request * covered the whole range of the protected object. On receiving a * conflicting request (any request while a write request is * effective, or any write request while some read ones are * effective), all requests granted in "cheating" mode are drained, * and the rangelock then switches to effectively keeping track of the * precise range of each new request. * * Normal sx implementation is not used to not bloat structures (most * important, vnodes) which embeds rangelocks. * * The cheating greatly helps very common pattern where file is first * written single-threaded, and then read by many processes. * * Lock is in cheat mode when RL_CHEAT_CHEATING bit is set in the * lock->head. Special cookies are returned in this mode, and * trylocks are same as normal locks but do not drain. */ static int rangelock_cheat = 1; SYSCTL_INT(_debug, OID_AUTO, rangelock_cheat, CTLFLAG_RWTUN, &rangelock_cheat, 0, ""); #define RL_CHEAT_MASK 0x7 #define RL_CHEAT_CHEATING 0x1 /* #define RL_CHEAT_RLOCKED 0x0 */ #define RL_CHEAT_WLOCKED 0x2 #define RL_CHEAT_DRAINING 0x4 #define RL_CHEAT_READER 0x8 #define RL_RET_CHEAT_RLOCKED 0x1100 #define RL_RET_CHEAT_WLOCKED 0x2200 static bool rangelock_cheat_lock(struct rangelock *lock, int locktype, bool trylock, void **cookie) { uintptr_t v, x; v = (uintptr_t)atomic_load_ptr(&lock->head); if ((v & RL_CHEAT_CHEATING) == 0) return (false); if ((v & RL_CHEAT_DRAINING) != 0) { drain: if (trylock) { *cookie = NULL; return (true); } sleepq_lock(&lock->head); drain1: DROP_GIANT(); for (;;) { v = (uintptr_t)atomic_load_ptr(&lock->head); if ((v & RL_CHEAT_DRAINING) == 0) break; sleepq_add(&lock->head, NULL, "ranged1", 0, 0); sleepq_wait(&lock->head, PRI_USER); sleepq_lock(&lock->head); } sleepq_release(&lock->head); PICKUP_GIANT(); return (false); } switch (locktype) { case RL_LOCK_READ: for (;;) { if ((v & RL_CHEAT_WLOCKED) != 0) { if (trylock) { *cookie = NULL; return (true); } x = v | RL_CHEAT_DRAINING; sleepq_lock(&lock->head); if (atomic_fcmpset_rel_ptr(&lock->head, &v, x) != 0) goto drain1; sleepq_release(&lock->head); /* Possibly forgive passed conflict */ - continue; + } else { + x = (v & ~RL_CHEAT_MASK) + RL_CHEAT_READER; + x |= RL_CHEAT_CHEATING; + if (atomic_fcmpset_acq_ptr(&lock->head, &v, + x) != 0) + break; } - x = (v & ~RL_CHEAT_MASK) + RL_CHEAT_READER; - x |= RL_CHEAT_CHEATING; - if (atomic_fcmpset_acq_ptr(&lock->head, &v, x) != 0) - break; if ((v & RL_CHEAT_CHEATING) == 0) return (false); if ((v & RL_CHEAT_DRAINING) != 0) goto drain; } *(uintptr_t *)cookie = RL_RET_CHEAT_RLOCKED; break; case RL_LOCK_WRITE: for (;;) { if ((v & ~RL_CHEAT_MASK) >= RL_CHEAT_READER || (v & RL_CHEAT_WLOCKED) != 0) { if (trylock) { *cookie = NULL; return (true); } x = v | RL_CHEAT_DRAINING; sleepq_lock(&lock->head); if (atomic_fcmpset_rel_ptr(&lock->head, &v, x) != 0) goto drain1; sleepq_release(&lock->head); /* Possibly forgive passed conflict */ - continue; + } else { + x = RL_CHEAT_WLOCKED | RL_CHEAT_CHEATING; + if (atomic_fcmpset_acq_ptr(&lock->head, &v, + x) != 0) + break; } - x = RL_CHEAT_WLOCKED | RL_CHEAT_CHEATING; - if (atomic_fcmpset_acq_ptr(&lock->head, &v, x) != 0) - break; if ((v & RL_CHEAT_CHEATING) == 0) return (false); if ((v & RL_CHEAT_DRAINING) != 0) goto drain; } *(uintptr_t *)cookie = RL_RET_CHEAT_WLOCKED; break; default: __assert_unreachable(); break; } return (true); } static bool rangelock_cheat_unlock(struct rangelock *lock, void *cookie) { uintptr_t v, x; v = (uintptr_t)atomic_load_ptr(&lock->head); if ((v & RL_CHEAT_CHEATING) == 0) return (false); MPASS((uintptr_t)cookie == RL_RET_CHEAT_WLOCKED || (uintptr_t)cookie == RL_RET_CHEAT_RLOCKED); switch ((uintptr_t)cookie) { case RL_RET_CHEAT_RLOCKED: for (;;) { MPASS((v & ~RL_CHEAT_MASK) >= RL_CHEAT_READER); MPASS((v & RL_CHEAT_WLOCKED) == 0); x = (v & ~RL_CHEAT_MASK) - RL_CHEAT_READER; if ((v & RL_CHEAT_DRAINING) != 0) { if (x != 0) { x |= RL_CHEAT_DRAINING | RL_CHEAT_CHEATING; if (atomic_fcmpset_rel_ptr(&lock->head, &v, x) != 0) break; } else { sleepq_lock(&lock->head); if (atomic_fcmpset_rel_ptr(&lock->head, &v, x) != 0) { sleepq_broadcast( &lock->head, SLEEPQ_SLEEP, 0, 0); sleepq_release(&lock->head); break; } sleepq_release(&lock->head); } } else { x |= RL_CHEAT_CHEATING; if (atomic_fcmpset_rel_ptr(&lock->head, &v, x) != 0) break; } } break; case RL_RET_CHEAT_WLOCKED: for (;;) { MPASS((v & RL_CHEAT_WLOCKED) != 0); if ((v & RL_CHEAT_DRAINING) != 0) { sleepq_lock(&lock->head); atomic_store_ptr(&lock->head, 0); sleepq_broadcast(&lock->head, SLEEPQ_SLEEP, 0, 0); sleepq_release(&lock->head); break; } else { if (atomic_fcmpset_ptr(&lock->head, &v, RL_CHEAT_CHEATING) != 0) break; } } break; default: __assert_unreachable(); break; } return (true); } static bool rangelock_cheat_destroy(struct rangelock *lock) { uintptr_t v; v = (uintptr_t)atomic_load_ptr(&lock->head); if ((v & RL_CHEAT_CHEATING) == 0) return (false); MPASS(v == RL_CHEAT_CHEATING); return (true); } /* * Implementation of range locks based on the paper * https://doi.org/10.1145/3342195.3387533 * arXiv:2006.12144v1 [cs.OS] 22 Jun 2020 * Scalable Range Locks for Scalable Address Spaces and Beyond * by Alex Kogan, Dave Dice, and Shady Issa */ static struct rl_q_entry *rl_e_unmark(const struct rl_q_entry *e); /* * rl_q_next links all granted ranges in the lock. We cannot free an * rl_q_entry while in the smr section, and cannot reuse rl_q_next * linkage since other threads might follow it even after CAS removed * the range. Use rl_q_free for local list of ranges to remove after * the smr section is dropped. */ struct rl_q_entry { struct rl_q_entry *rl_q_next; struct rl_q_entry *rl_q_free; off_t rl_q_start, rl_q_end; int rl_q_flags; #ifdef INVARIANTS struct thread *rl_q_owner; #endif }; static uma_zone_t rl_entry_zone; static smr_t rl_smr; static void rangelock_sys_init(void) { rl_entry_zone = uma_zcreate("rl_entry", sizeof(struct rl_q_entry), NULL, NULL, NULL, NULL, UMA_ALIGNOF(struct rl_q_entry), UMA_ZONE_SMR); rl_smr = uma_zone_get_smr(rl_entry_zone); } SYSINIT(rl, SI_SUB_LOCK, SI_ORDER_ANY, rangelock_sys_init, NULL); static struct rl_q_entry * rlqentry_alloc(vm_ooffset_t start, vm_ooffset_t end, int flags) { struct rl_q_entry *e; struct thread *td; td = curthread; if (td->td_rlqe != NULL) { e = td->td_rlqe; td->td_rlqe = NULL; } else { e = uma_zalloc_smr(rl_entry_zone, M_WAITOK); } e->rl_q_next = NULL; e->rl_q_free = NULL; e->rl_q_start = start; e->rl_q_end = end; e->rl_q_flags = flags; #ifdef INVARIANTS e->rl_q_owner = curthread; #endif return (e); } void rangelock_entry_free(struct rl_q_entry *e) { uma_zfree_smr(rl_entry_zone, e); } void rangelock_init(struct rangelock *lock) { lock->sleepers = false; atomic_store_ptr(&lock->head, rangelock_cheat ? RL_CHEAT_CHEATING : 0); } void rangelock_destroy(struct rangelock *lock) { struct rl_q_entry *e, *ep; MPASS(!lock->sleepers); if (rangelock_cheat_destroy(lock)) return; for (e = (struct rl_q_entry *)atomic_load_ptr(&lock->head); e != NULL; e = rl_e_unmark(ep)) { ep = atomic_load_ptr(&e->rl_q_next); uma_zfree_smr(rl_entry_zone, e); } } static bool rl_e_is_marked(const struct rl_q_entry *e) { return (((uintptr_t)e & 1) != 0); } static struct rl_q_entry * rl_e_unmark_unchecked(const struct rl_q_entry *e) { return ((struct rl_q_entry *)((uintptr_t)e & ~1)); } static struct rl_q_entry * rl_e_unmark(const struct rl_q_entry *e) { MPASS(rl_e_is_marked(e)); return (rl_e_unmark_unchecked(e)); } static void rl_e_mark(struct rl_q_entry *e) { #if defined(INVARIANTS) && defined(__LP64__) int r = atomic_testandset_long((uintptr_t *)&e->rl_q_next, 0); MPASS(r == 0); #else atomic_set_ptr((uintptr_t *)&e->rl_q_next, 1); #endif } static struct rl_q_entry * rl_q_load(struct rl_q_entry **p) { return ((struct rl_q_entry *)atomic_load_acq_ptr((uintptr_t *)p)); } static bool rl_e_is_rlock(const struct rl_q_entry *e) { return ((e->rl_q_flags & RL_LOCK_TYPE_MASK) == RL_LOCK_READ); } static void rangelock_unlock_int(struct rangelock *lock, struct rl_q_entry *e) { bool sleepers; MPASS(lock != NULL && e != NULL); MPASS(!rl_e_is_marked(rl_q_load(&e->rl_q_next))); MPASS(e->rl_q_owner == curthread); rl_e_mark(e); sleepers = lock->sleepers; lock->sleepers = false; if (sleepers) sleepq_broadcast(&lock->sleepers, SLEEPQ_SLEEP, 0, 0); } void rangelock_unlock(struct rangelock *lock, void *cookie) { if (rangelock_cheat_unlock(lock, cookie)) return; sleepq_lock(&lock->sleepers); rangelock_unlock_int(lock, cookie); sleepq_release(&lock->sleepers); } /* * result: -1 if e1 before e2, or both locks are readers and e1 * starts before or at e2 * 1 if e1 after e2, or both locks are readers and e1 * starts after e2 * 0 if e1 and e2 overlap and at least one lock is writer */ static int rl_e_compare(const struct rl_q_entry *e1, const struct rl_q_entry *e2) { bool rds; if (e1 == NULL) return (1); if (e2->rl_q_start >= e1->rl_q_end) return (-1); rds = rl_e_is_rlock(e1) && rl_e_is_rlock(e2); if (e2->rl_q_start >= e1->rl_q_start && rds) return (-1); if (e1->rl_q_start >= e2->rl_q_end) return (1); if (e1->rl_q_start >= e2->rl_q_start && rds) return (1); return (0); } static void rl_insert_sleep(struct rangelock *lock) { smr_exit(rl_smr); DROP_GIANT(); lock->sleepers = true; sleepq_add(&lock->sleepers, NULL, "rangelk", 0, 0); sleepq_wait(&lock->sleepers, PRI_USER); PICKUP_GIANT(); smr_enter(rl_smr); } static bool rl_q_cas(struct rl_q_entry **prev, struct rl_q_entry *old, struct rl_q_entry *new) { return (atomic_cmpset_rel_ptr((uintptr_t *)prev, (uintptr_t)old, (uintptr_t)new) != 0); } enum RL_INSERT_RES { RL_TRYLOCK_FAILED, RL_LOCK_SUCCESS, RL_LOCK_RETRY, }; static enum RL_INSERT_RES rl_r_validate(struct rangelock *lock, struct rl_q_entry *e, bool trylock, struct rl_q_entry **free) { struct rl_q_entry *cur, *next, **prev; prev = &e->rl_q_next; cur = rl_q_load(prev); MPASS(!rl_e_is_marked(cur)); /* nobody can unlock e yet */ for (;;) { if (cur == NULL || cur->rl_q_start > e->rl_q_end) return (RL_LOCK_SUCCESS); next = rl_q_load(&cur->rl_q_next); if (rl_e_is_marked(next)) { next = rl_e_unmark(next); if (rl_q_cas(prev, cur, next)) { cur->rl_q_free = *free; *free = cur; } cur = next; continue; } if (rl_e_is_rlock(cur)) { prev = &cur->rl_q_next; cur = rl_e_unmark_unchecked(rl_q_load(prev)); continue; } if (!rl_e_is_marked(rl_q_load(&cur->rl_q_next))) { sleepq_lock(&lock->sleepers); if (rl_e_is_marked(rl_q_load(&cur->rl_q_next))) { sleepq_release(&lock->sleepers); continue; } rangelock_unlock_int(lock, e); if (trylock) { sleepq_release(&lock->sleepers); return (RL_TRYLOCK_FAILED); } rl_insert_sleep(lock); return (RL_LOCK_RETRY); } } } static enum RL_INSERT_RES rl_w_validate(struct rangelock *lock, struct rl_q_entry *e, bool trylock, struct rl_q_entry **free) { struct rl_q_entry *cur, *next, **prev; prev = (struct rl_q_entry **)&lock->head; cur = rl_q_load(prev); MPASS(!rl_e_is_marked(cur)); /* head is not marked */ for (;;) { if (cur == e) return (RL_LOCK_SUCCESS); next = rl_q_load(&cur->rl_q_next); if (rl_e_is_marked(next)) { next = rl_e_unmark(next); if (rl_q_cas(prev, cur, next)) { cur->rl_q_next = *free; *free = cur; } cur = next; continue; } if (cur->rl_q_end <= e->rl_q_start) { prev = &cur->rl_q_next; cur = rl_e_unmark_unchecked(rl_q_load(prev)); continue; } sleepq_lock(&lock->sleepers); rangelock_unlock_int(lock, e); if (trylock) { sleepq_release(&lock->sleepers); return (RL_TRYLOCK_FAILED); } rl_insert_sleep(lock); return (RL_LOCK_RETRY); } } static enum RL_INSERT_RES rl_insert(struct rangelock *lock, struct rl_q_entry *e, bool trylock, struct rl_q_entry **free) { struct rl_q_entry *cur, *next, **prev; int r; again: prev = (struct rl_q_entry **)&lock->head; cur = rl_q_load(prev); if (cur == NULL && rl_q_cas(prev, NULL, e)) return (RL_LOCK_SUCCESS); for (;;) { if (cur != NULL) { if (rl_e_is_marked(cur)) goto again; next = rl_q_load(&cur->rl_q_next); if (rl_e_is_marked(next)) { next = rl_e_unmark(next); if (rl_q_cas(prev, cur, next)) { #ifdef INVARIANTS cur->rl_q_owner = NULL; #endif cur->rl_q_free = *free; *free = cur; } cur = next; continue; } } r = rl_e_compare(cur, e); if (r == -1) { prev = &cur->rl_q_next; cur = rl_q_load(prev); } else if (r == 0) { sleepq_lock(&lock->sleepers); if (__predict_false(rl_e_is_marked(rl_q_load( &cur->rl_q_next)))) { sleepq_release(&lock->sleepers); continue; } if (trylock) { sleepq_release(&lock->sleepers); return (RL_TRYLOCK_FAILED); } rl_insert_sleep(lock); /* e is still valid */ goto again; } else /* r == 1 */ { e->rl_q_next = cur; if (rl_q_cas(prev, cur, e)) { atomic_thread_fence_acq(); return (rl_e_is_rlock(e) ? rl_r_validate(lock, e, trylock, free) : rl_w_validate(lock, e, trylock, free)); } /* Reset rl_q_next in case we hit fast path. */ e->rl_q_next = NULL; cur = rl_q_load(prev); } } } static struct rl_q_entry * rangelock_lock_int(struct rangelock *lock, bool trylock, vm_ooffset_t start, vm_ooffset_t end, int locktype) { struct rl_q_entry *e, *free, *x, *xp; struct thread *td; void *cookie; enum RL_INSERT_RES res; if (rangelock_cheat_lock(lock, locktype, trylock, &cookie)) return (cookie); td = curthread; for (res = RL_LOCK_RETRY; res == RL_LOCK_RETRY;) { free = NULL; e = rlqentry_alloc(start, end, locktype); smr_enter(rl_smr); res = rl_insert(lock, e, trylock, &free); smr_exit(rl_smr); if (res == RL_TRYLOCK_FAILED) { MPASS(trylock); e->rl_q_free = free; free = e; e = NULL; } for (x = free; x != NULL; x = xp) { MPASS(!rl_e_is_marked(x)); xp = x->rl_q_free; MPASS(!rl_e_is_marked(xp)); if (td->td_rlqe == NULL) { smr_synchronize(rl_smr); td->td_rlqe = x; } else { uma_zfree_smr(rl_entry_zone, x); } } } return (e); } void * rangelock_rlock(struct rangelock *lock, vm_ooffset_t start, vm_ooffset_t end) { return (rangelock_lock_int(lock, false, start, end, RL_LOCK_READ)); } void * rangelock_tryrlock(struct rangelock *lock, vm_ooffset_t start, vm_ooffset_t end) { return (rangelock_lock_int(lock, true, start, end, RL_LOCK_READ)); } void * rangelock_wlock(struct rangelock *lock, vm_ooffset_t start, vm_ooffset_t end) { return (rangelock_lock_int(lock, false, start, end, RL_LOCK_WRITE)); } void * rangelock_trywlock(struct rangelock *lock, vm_ooffset_t start, vm_ooffset_t end) { return (rangelock_lock_int(lock, true, start, end, RL_LOCK_WRITE)); } #ifdef INVARIANT_SUPPORT void _rangelock_cookie_assert(void *cookie, int what, const char *file, int line) { } #endif /* INVARIANT_SUPPORT */ #include "opt_ddb.h" #ifdef DDB #include DB_SHOW_COMMAND(rangelock, db_show_rangelock) { struct rangelock *lock; struct rl_q_entry *e, *x; uintptr_t v; if (!have_addr) { db_printf("show rangelock addr\n"); return; } lock = (struct rangelock *)addr; db_printf("rangelock %p sleepers %d\n", lock, lock->sleepers); v = lock->head; if ((v & RL_CHEAT_CHEATING) != 0) { db_printf(" cheating head %#jx\n", (uintmax_t)v); return; } for (e = (struct rl_q_entry *)(lock->head);;) { x = rl_e_is_marked(e) ? rl_e_unmark(e) : e; if (x == NULL) break; db_printf(" entry %p marked %d %d start %#jx end %#jx " "flags %x next %p", e, rl_e_is_marked(e), rl_e_is_marked(x->rl_q_next), x->rl_q_start, x->rl_q_end, x->rl_q_flags, x->rl_q_next); #ifdef INVARIANTS db_printf(" owner %p (%d)", x->rl_q_owner, x->rl_q_owner != NULL ? x->rl_q_owner->td_tid : -1); #endif db_printf("\n"); e = x->rl_q_next; } } #endif /* DDB */