X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;fp=urcu.c;h=0000000000000000000000000000000000000000;hp=a5568bdbd075ed1edc4539dec460c7cce40ee590;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332 diff --git a/urcu.c b/urcu.c deleted file mode 100644 index a5568bd..0000000 --- a/urcu.c +++ /dev/null @@ -1,605 +0,0 @@ -/* - * urcu.c - * - * Userspace RCU library - * - * Copyright (c) 2009 Mathieu Desnoyers - * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. - * - * This library is free software; you can redistribute it and/or - * modify it under the terms of the GNU Lesser General Public - * License as published by the Free Software Foundation; either - * version 2.1 of the License, or (at your option) any later version. - * - * This library is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - * Lesser General Public License for more details. - * - * You should have received a copy of the GNU Lesser General Public - * License along with this library; if not, write to the Free Software - * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA - * - * IBM's contributions to this file may be relicensed under LGPLv2 or later. - */ - -#define _BSD_SOURCE -#define _GNU_SOURCE -#define _LGPL_SOURCE -#define _DEFAULT_SOURCE -#include -#include -#include -#include -#include -#include -#include -#include -#include - -#include "urcu/arch.h" -#include "urcu/wfcqueue.h" -#include "urcu/map/urcu.h" -#include "urcu/static/urcu.h" -#include "urcu-pointer.h" -#include "urcu/tls-compat.h" - -#include "urcu-die.h" -#include "urcu-wait.h" - -/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ -#undef _LGPL_SOURCE -#include "urcu.h" -#define _LGPL_SOURCE - -/* - * If a reader is really non-cooperative and refuses to commit its - * rcu_active_readers count to memory (there is no barrier in the reader - * per-se), kick it after 10 loops waiting for it. - */ -#define KICK_READER_LOOPS 10 - -/* - * Active attempts to check for reader Q.S. before calling futex(). - */ -#define RCU_QS_ACTIVE_ATTEMPTS 100 - -/* If the headers do not support membarrier system call, fall back on RCU_MB */ -#ifdef __NR_membarrier -# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__) -#else -# define membarrier(...) -ENOSYS -#endif - -enum membarrier_cmd { - MEMBARRIER_CMD_QUERY = 0, - MEMBARRIER_CMD_SHARED = (1 << 0), -}; - -#ifdef RCU_MEMBARRIER -static int init_done; -int rcu_has_sys_membarrier; - -void __attribute__((constructor)) rcu_init(void); -#endif - -#ifdef RCU_MB -void rcu_init(void) -{ -} -#endif - -#ifdef RCU_SIGNAL -static int init_done; - -void __attribute__((constructor)) rcu_init(void); -void __attribute__((destructor)) rcu_exit(void); -#endif - -/* - * rcu_gp_lock ensures mutual exclusion between threads calling - * synchronize_rcu(). - */ -static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; -/* - * rcu_registry_lock ensures mutual exclusion between threads - * registering and unregistering themselves to/from the registry, and - * with threads reading that registry from synchronize_rcu(). However, - * this lock is not held all the way through the completion of awaiting - * for the grace period. It is sporadically released between iterations - * on the registry. - * rcu_registry_lock may nest inside rcu_gp_lock. - */ -static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; -struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT }; - -/* - * Written to only by each individual reader. Read by both the reader and the - * writers. - */ -DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); - -static CDS_LIST_HEAD(registry); - -/* - * Queue keeping threads awaiting to wait for a grace period. Contains - * struct gp_waiters_thread objects. - */ -static DEFINE_URCU_WAIT_QUEUE(gp_waiters); - -static void mutex_lock(pthread_mutex_t *mutex) -{ - int ret; - -#ifndef DISTRUST_SIGNALS_EXTREME - ret = pthread_mutex_lock(mutex); - if (ret) - urcu_die(ret); -#else /* #ifndef DISTRUST_SIGNALS_EXTREME */ - while ((ret = pthread_mutex_trylock(mutex)) != 0) { - if (ret != EBUSY && ret != EINTR) - urcu_die(ret); - if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) { - cmm_smp_mb(); - _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); - cmm_smp_mb(); - } - (void) poll(NULL, 0, 10); - } -#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ -} - -static void mutex_unlock(pthread_mutex_t *mutex) -{ - int ret; - - ret = pthread_mutex_unlock(mutex); - if (ret) - urcu_die(ret); -} - -#ifdef RCU_MEMBARRIER -static void smp_mb_master(void) -{ - if (caa_likely(rcu_has_sys_membarrier)) - (void) membarrier(MEMBARRIER_CMD_SHARED, 0); - else - cmm_smp_mb(); -} -#endif - -#ifdef RCU_MB -static void smp_mb_master(void) -{ - cmm_smp_mb(); -} -#endif - -#ifdef RCU_SIGNAL -static void force_mb_all_readers(void) -{ - struct rcu_reader *index; - - /* - * Ask for each threads to execute a cmm_smp_mb() so we can consider the - * compiler barriers around rcu read lock as real memory barriers. - */ - if (cds_list_empty(®istry)) - return; - /* - * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs - * a cache flush on architectures with non-coherent cache. Let's play - * safe and don't assume anything : we use cmm_smp_mc() to make sure the - * cache flush is enforced. - */ - cds_list_for_each_entry(index, ®istry, node) { - CMM_STORE_SHARED(index->need_mb, 1); - pthread_kill(index->tid, SIGRCU); - } - /* - * Wait for sighandler (and thus mb()) to execute on every thread. - * - * Note that the pthread_kill() will never be executed on systems - * that correctly deliver signals in a timely manner. However, it - * is not uncommon for kernels to have bugs that can result in - * lost or unduly delayed signals. - * - * If you are seeing the below pthread_kill() executing much at - * all, we suggest testing the underlying kernel and filing the - * relevant bug report. For Linux kernels, we recommend getting - * the Linux Test Project (LTP). - */ - cds_list_for_each_entry(index, ®istry, node) { - while (CMM_LOAD_SHARED(index->need_mb)) { - pthread_kill(index->tid, SIGRCU); - (void) poll(NULL, 0, 1); - } - } - cmm_smp_mb(); /* read ->need_mb before ending the barrier */ -} - -static void smp_mb_master(void) -{ - force_mb_all_readers(); -} -#endif /* #ifdef RCU_SIGNAL */ - -/* - * synchronize_rcu() waiting. Single thread. - * Always called with rcu_registry lock held. Releases this lock and - * grabs it again. Holds the lock when it returns. - */ -static void wait_gp(void) -{ - /* - * Read reader_gp before read futex. smp_mb_master() needs to - * be called with the rcu registry lock held in RCU_SIGNAL - * flavor. - */ - smp_mb_master(); - /* Temporarily unlock the registry lock. */ - mutex_unlock(&rcu_registry_lock); - if (uatomic_read(&rcu_gp.futex) != -1) - goto end; - while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, - NULL, NULL, 0)) { - switch (errno) { - case EWOULDBLOCK: - /* Value already changed. */ - goto end; - case EINTR: - /* Retry if interrupted by signal. */ - break; /* Get out of switch. */ - default: - /* Unexpected error. */ - urcu_die(errno); - } - } -end: - /* - * Re-lock the registry lock before the next loop. - */ - mutex_lock(&rcu_registry_lock); -} - -/* - * Always called with rcu_registry lock held. Releases this lock between - * iterations and grabs it again. Holds the lock when it returns. - */ -static void wait_for_readers(struct cds_list_head *input_readers, - struct cds_list_head *cur_snap_readers, - struct cds_list_head *qsreaders) -{ - unsigned int wait_loops = 0; - struct rcu_reader *index, *tmp; -#ifdef HAS_INCOHERENT_CACHES - unsigned int wait_gp_loops = 0; -#endif /* HAS_INCOHERENT_CACHES */ - - /* - * Wait for each thread URCU_TLS(rcu_reader).ctr to either - * indicate quiescence (not nested), or observe the current - * rcu_gp.ctr value. - */ - for (;;) { - if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) - wait_loops++; - if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_dec(&rcu_gp.futex); - /* Write futex before read reader_gp */ - smp_mb_master(); - } - - cds_list_for_each_entry_safe(index, tmp, input_readers, node) { - switch (rcu_reader_state(&index->ctr)) { - case RCU_READER_ACTIVE_CURRENT: - if (cur_snap_readers) { - cds_list_move(&index->node, - cur_snap_readers); - break; - } - /* Fall-through */ - case RCU_READER_INACTIVE: - cds_list_move(&index->node, qsreaders); - break; - case RCU_READER_ACTIVE_OLD: - /* - * Old snapshot. Leaving node in - * input_readers will make us busy-loop - * until the snapshot becomes current or - * the reader becomes inactive. - */ - break; - } - } - -#ifndef HAS_INCOHERENT_CACHES - if (cds_list_empty(input_readers)) { - if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - /* Read reader_gp before write futex */ - smp_mb_master(); - uatomic_set(&rcu_gp.futex, 0); - } - break; - } else { - if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - /* wait_gp unlocks/locks registry lock. */ - wait_gp(); - } else { - /* Temporarily unlock the registry lock. */ - mutex_unlock(&rcu_registry_lock); - caa_cpu_relax(); - /* - * Re-lock the registry lock before the - * next loop. - */ - mutex_lock(&rcu_registry_lock); - } - } -#else /* #ifndef HAS_INCOHERENT_CACHES */ - /* - * BUSY-LOOP. Force the reader thread to commit its - * URCU_TLS(rcu_reader).ctr update to memory if we wait - * for too long. - */ - if (cds_list_empty(input_readers)) { - if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - /* Read reader_gp before write futex */ - smp_mb_master(); - uatomic_set(&rcu_gp.futex, 0); - } - break; - } else { - if (wait_gp_loops == KICK_READER_LOOPS) { - smp_mb_master(); - wait_gp_loops = 0; - } - if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - /* wait_gp unlocks/locks registry lock. */ - wait_gp(); - wait_gp_loops++; - } else { - /* Temporarily unlock the registry lock. */ - mutex_unlock(&rcu_registry_lock); - caa_cpu_relax(); - /* - * Re-lock the registry lock before the - * next loop. - */ - mutex_lock(&rcu_registry_lock); - } - } -#endif /* #else #ifndef HAS_INCOHERENT_CACHES */ - } -} - -void synchronize_rcu(void) -{ - CDS_LIST_HEAD(cur_snap_readers); - CDS_LIST_HEAD(qsreaders); - DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); - struct urcu_waiters waiters; - - /* - * Add ourself to gp_waiters queue of threads awaiting to wait - * for a grace period. Proceed to perform the grace period only - * if we are the first thread added into the queue. - * The implicit memory barrier before urcu_wait_add() - * orders prior memory accesses of threads put into the wait - * queue before their insertion into the wait queue. - */ - if (urcu_wait_add(&gp_waiters, &wait) != 0) { - /* Not first in queue: will be awakened by another thread. */ - urcu_adaptative_busy_wait(&wait); - /* Order following memory accesses after grace period. */ - cmm_smp_mb(); - return; - } - /* We won't need to wake ourself up */ - urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); - - mutex_lock(&rcu_gp_lock); - - /* - * Move all waiters into our local queue. - */ - urcu_move_waiters(&waiters, &gp_waiters); - - mutex_lock(&rcu_registry_lock); - - if (cds_list_empty(®istry)) - goto out; - - /* - * All threads should read qparity before accessing data structure - * where new ptr points to. Must be done within rcu_registry_lock - * because it iterates on reader threads. - */ - /* Write new ptr before changing the qparity */ - smp_mb_master(); - - /* - * Wait for readers to observe original parity or be quiescent. - * wait_for_readers() can release and grab again rcu_registry_lock - * interally. - */ - wait_for_readers(®istry, &cur_snap_readers, &qsreaders); - - /* - * Must finish waiting for quiescent state for original parity before - * 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 - * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr. - */ - cmm_barrier(); - - /* - * Adding a cmm_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. - */ - cmm_smp_mb(); - - /* Switch parity: 0 -> 1, 1 -> 0 */ - CMM_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. - */ - cmm_barrier(); - - /* - * - * Adding a cmm_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. - */ - cmm_smp_mb(); - - /* - * Wait for readers to observe new parity or be quiescent. - * wait_for_readers() can release and grab again rcu_registry_lock - * interally. - */ - wait_for_readers(&cur_snap_readers, NULL, &qsreaders); - - /* - * Put quiescent reader list back into registry. - */ - cds_list_splice(&qsreaders, ®istry); - - /* - * Finish waiting for reader threads before letting the old ptr - * being freed. Must be done within rcu_registry_lock because it - * iterates on reader threads. - */ - smp_mb_master(); -out: - mutex_unlock(&rcu_registry_lock); - mutex_unlock(&rcu_gp_lock); - - /* - * Wakeup waiters only after we have completed the grace period - * and have ensured the memory barriers at the end of the grace - * period have been issued. - */ - urcu_wake_all_waiters(&waiters); -} - -/* - * library wrappers to be used by non-LGPL compatible source code. - */ - -void rcu_read_lock(void) -{ - _rcu_read_lock(); -} - -void rcu_read_unlock(void) -{ - _rcu_read_unlock(); -} - -int rcu_read_ongoing(void) -{ - return _rcu_read_ongoing(); -} - -void rcu_register_thread(void) -{ - URCU_TLS(rcu_reader).tid = pthread_self(); - assert(URCU_TLS(rcu_reader).need_mb == 0); - assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK)); - - mutex_lock(&rcu_registry_lock); - assert(!URCU_TLS(rcu_reader).registered); - URCU_TLS(rcu_reader).registered = 1; - rcu_init(); /* In case gcc does not support constructor attribute */ - cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); - mutex_unlock(&rcu_registry_lock); -} - -void rcu_unregister_thread(void) -{ - mutex_lock(&rcu_registry_lock); - assert(URCU_TLS(rcu_reader).registered); - URCU_TLS(rcu_reader).registered = 0; - cds_list_del(&URCU_TLS(rcu_reader).node); - mutex_unlock(&rcu_registry_lock); -} - -#ifdef RCU_MEMBARRIER -void rcu_init(void) -{ - int ret; - - if (init_done) - return; - init_done = 1; - ret = membarrier(MEMBARRIER_CMD_QUERY, 0); - if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) { - rcu_has_sys_membarrier = 1; - } -} -#endif - -#ifdef RCU_SIGNAL -static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) -{ - /* - * Executing this cmm_smp_mb() is the only purpose of this signal handler. - * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is - * executed on. - */ - cmm_smp_mb(); - _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); - cmm_smp_mb(); -} - -/* - * rcu_init constructor. Called when the library is linked, but also when - * reader threads are calling rcu_register_thread(). - * Should only be called by a single thread at a given time. This is ensured by - * holing the rcu_registry_lock from rcu_register_thread() or by running - * at library load time, which should not be executed by multiple - * threads nor concurrently with rcu_register_thread() anyway. - */ -void rcu_init(void) -{ - struct sigaction act; - int ret; - - if (init_done) - return; - init_done = 1; - - act.sa_sigaction = sigrcu_handler; - act.sa_flags = SA_SIGINFO | SA_RESTART; - sigemptyset(&act.sa_mask); - ret = sigaction(SIGRCU, &act, NULL); - if (ret) - urcu_die(errno); -} - -void rcu_exit(void) -{ - /* - * Don't unregister the SIGRCU signal handler anymore, because - * call_rcu threads could still be using it shortly before the - * application exits. - * Assertion disabled because call_rcu threads are now rcu - * readers, and left running at exit. - * assert(cds_list_empty(®istry)); - */ -} - -#endif /* #ifdef RCU_SIGNAL */ - -DEFINE_RCU_FLAVOR(rcu_flavor); - -#include "urcu-call-rcu-impl.h" -#include "urcu-defer-impl.h"