X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=918d2742a0429683c11e42c60c77187bc908e862;hp=6e9589145cf789a06c00aa988cb01d8c3dcb27fa;hb=eaf2c3f4b9041d2a6a85d7f9e56f6014603367d4;hpb=6abb4bd53503c325dc94b0c0f60b44b9550b462f diff --git a/urcu.c b/urcu.c index 6e95891..918d274 100644 --- a/urcu.c +++ b/urcu.c @@ -3,7 +3,7 @@ * * Userspace RCU library * - * Copyright (c) 2009 Mathieu Desnoyers + * Copyright (c) 2009 Mathieu Desnoyers * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. * * This library is free software; you can redistribute it and/or @@ -67,7 +67,7 @@ int gp_futex; * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path. * Written to only by writer with mutex taken. Read by both writer and readers. */ -long rcu_gp_ctr = RCU_GP_COUNT; +unsigned long rcu_gp_ctr = RCU_GP_COUNT; /* * Written to only by each individual reader. Read by both the reader and the @@ -99,9 +99,9 @@ static void mutex_lock(pthread_mutex_t *mutex) perror("Error in pthread mutex lock"); exit(-1); } - if (rcu_reader.need_mb) { + if (LOAD_SHARED(rcu_reader.need_mb)) { smp_mb(); - rcu_reader.need_mb = 0; + _STORE_SHARED(rcu_reader.need_mb, 0); smp_mb(); } poll(NULL,0,10); @@ -120,16 +120,8 @@ static void mutex_unlock(pthread_mutex_t *mutex) } } -/* - * called with rcu_gp_lock held. - */ -static void switch_next_rcu_qparity(void) -{ - STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); -} - #ifdef RCU_MEMBARRIER -static void smp_mb_heavy(void) +static void smp_mb_master(int group) { if (likely(has_sys_membarrier)) membarrier(MEMBARRIER_EXPEDITED); @@ -139,7 +131,7 @@ static void smp_mb_heavy(void) #endif #ifdef RCU_MB -static void smp_mb_heavy(void) +static void smp_mb_master(int group) { smp_mb(); } @@ -162,9 +154,8 @@ static void force_mb_all_readers(void) * safe and don't assume anything : we use smp_mc() to make sure the * cache flush is enforced. */ - list_for_each_entry(index, ®istry, head) { - index->need_mb = 1; - smp_mc(); /* write need_mb before sending the signal */ + list_for_each_entry(index, ®istry, node) { + STORE_SHARED(index->need_mb, 1); pthread_kill(index->tid, SIGRCU); } /* @@ -180,8 +171,8 @@ static void force_mb_all_readers(void) * relevant bug report. For Linux kernels, we recommend getting * the Linux Test Project (LTP). */ - list_for_each_entry(index, ®istry, head) { - while (index->need_mb) { + list_for_each_entry(index, ®istry, node) { + while (LOAD_SHARED(index->need_mb)) { pthread_kill(index->tid, SIGRCU); poll(NULL, 0, 1); } @@ -189,7 +180,7 @@ static void force_mb_all_readers(void) smp_mb(); /* read ->need_mb before ending the barrier */ } -static void smp_mb_heavy(void) +static void smp_mb_master(int group) { force_mb_all_readers(); } @@ -201,20 +192,37 @@ static void smp_mb_heavy(void) static void wait_gp(void) { /* Read reader_gp before read futex */ - smp_mb_heavy(); + smp_mb_master(RCU_MB_GROUP); if (uatomic_read(&gp_futex) == -1) futex_async(&gp_futex, FUTEX_WAIT, -1, NULL, NULL, 0); } -void wait_for_quiescent_state(void) +void update_counter_and_wait(void) { LIST_HEAD(qsreaders); int wait_loops = 0; struct rcu_reader *index, *tmp; - if (list_empty(®istry)) - return; + /* Switch parity: 0 -> 1, 1 -> 0 */ + STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); + + /* + * Must commit rcu_gp_ctr update to memory before waiting for quiescent + * state. Failure to do so could result in the writer waiting forever + * while new readers are always accessing data (no progress). Enforce + * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr. + */ + barrier(); + + /* + * + * Adding a smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. + */ + smp_mb(); + /* * Wait for each thread rcu_reader.ctr count to become 0. */ @@ -223,19 +231,19 @@ void wait_for_quiescent_state(void) if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { uatomic_dec(&gp_futex); /* Write futex before read reader_gp */ - smp_mb_heavy(); + smp_mb_master(RCU_MB_GROUP); } - list_for_each_entry_safe(index, tmp, ®istry, head) { - if (!rcu_old_gp_ongoing(&index->ctr)) - list_move(&index->head, &qsreaders); + list_for_each_entry_safe(index, tmp, ®istry, node) { + if (!rcu_gp_ongoing(&index->ctr)) + list_move(&index->node, &qsreaders); } #ifndef HAS_INCOHERENT_CACHES if (list_empty(®istry)) { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb_heavy(); + smp_mb_master(RCU_MB_GROUP); uatomic_set(&gp_futex, 0); } break; @@ -253,7 +261,7 @@ void wait_for_quiescent_state(void) if (list_empty(®istry)) { if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ - smp_mb_heavy(); + smp_mb_master(RCU_MB_GROUP); uatomic_set(&gp_futex, 0); } break; @@ -263,7 +271,7 @@ void wait_for_quiescent_state(void) wait_gp(); break; /* only escape switch */ case KICK_READER_LOOPS: - smp_mb_heavy(); + smp_mb_master(RCU_MB_GROUP); wait_loops = 0; break; /* only escape switch */ default: @@ -280,58 +288,28 @@ void synchronize_rcu(void) { mutex_lock(&rcu_gp_lock); + if (list_empty(®istry)) + goto out; + /* All threads should read qparity before accessing data structure * where new ptr points to. Must be done within rcu_gp_lock because it * iterates on reader threads.*/ /* Write new ptr before changing the qparity */ - smp_mb_heavy(); - - switch_next_rcu_qparity(); /* 0 -> 1 */ - - /* - * Must commit qparity update to memory before waiting for parity - * 0 quiescent state. Failure to do so could result in the writer - * waiting forever while new readers are always accessing data (no - * progress). - * Ensured by STORE_SHARED and LOAD_SHARED. - */ - - /* - * Adding a smp_mb() which is _not_ formally required, but makes the - * model easier to understand. It does not have a big performance impact - * anyway, given this is the write-side. - */ - smp_mb(); + smp_mb_master(RCU_MB_GROUP); /* * Wait for previous parity to be empty of readers. */ - wait_for_quiescent_state(); /* Wait readers in parity 0 */ + update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ /* * Must finish waiting for quiescent state for parity 0 before - * committing qparity update to memory. Failure to do so could result in - * the writer waiting forever while new readers are always accessing - * data (no progress). - * Ensured by STORE_SHARED and LOAD_SHARED. - */ - - /* - * Adding a smp_mb() which is _not_ formally required, but makes the - * model easier to understand. It does not have a big performance impact - * anyway, given this is the write-side. - */ - smp_mb(); - - switch_next_rcu_qparity(); /* 1 -> 0 */ - - /* - * Must commit qparity update to memory before waiting for parity - * 1 quiescent state. Failure to do so could result in the writer - * waiting forever while new readers are always accessing data (no - * progress). - * Ensured by STORE_SHARED and LOAD_SHARED. + * committing next rcu_gp_ctr update to memory. Failure to do so could + * result in the writer waiting forever while new readers are always + * accessing data (no progress). Enforce compiler-order of load + * rcu_reader ctr before store to rcu_gp_ctr. */ + barrier(); /* * Adding a smp_mb() which is _not_ formally required, but makes the @@ -343,13 +321,13 @@ void synchronize_rcu(void) /* * Wait for previous parity to be empty of readers. */ - wait_for_quiescent_state(); /* Wait readers in parity 1 */ + update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ /* Finish waiting for reader threads before letting the old ptr being * freed. Must be done within rcu_gp_lock because it iterates on reader * threads. */ - smp_mb_heavy(); - + smp_mb_master(RCU_MB_GROUP); +out: mutex_unlock(&rcu_gp_lock); } @@ -371,18 +349,18 @@ void rcu_register_thread(void) { rcu_reader.tid = pthread_self(); assert(rcu_reader.need_mb == 0); - assert(rcu_reader.ctr == 0); + assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK)); mutex_lock(&rcu_gp_lock); rcu_init(); /* In case gcc does not support constructor attribute */ - list_add(&rcu_reader.head, ®istry); + list_add(&rcu_reader.node, ®istry); mutex_unlock(&rcu_gp_lock); } void rcu_unregister_thread(void) { mutex_lock(&rcu_gp_lock); - list_del(&rcu_reader.head); + list_del(&rcu_reader.node); mutex_unlock(&rcu_gp_lock); } @@ -406,7 +384,7 @@ static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) * executed on. */ smp_mb(); - rcu_reader.need_mb = 0; + _STORE_SHARED(rcu_reader.need_mb, 0); smp_mb(); }