--- /dev/null
+/*
+ * urcu-bp.c
+ *
+ * Userspace RCU library, "bulletproof" version.
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * 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 _LGPL_SOURCE
+#include <stdio.h>
+#include <pthread.h>
+#include <signal.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <poll.h>
+#include <unistd.h>
+#include <sys/mman.h>
+
+#include "urcu/arch.h"
+#include "urcu/wfcqueue.h"
+#include "urcu/map/urcu-bp.h"
+#include "urcu/static/urcu-bp.h"
+#include "urcu-pointer.h"
+#include "urcu/tls-compat.h"
+
+#include "urcu-die.h"
+
+/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
+#undef _LGPL_SOURCE
+#include "urcu-bp.h"
+#define _LGPL_SOURCE
+
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+
+#ifdef __linux__
+static
+void *mremap_wrapper(void *old_address, size_t old_size,
+ size_t new_size, int flags)
+{
+ return mremap(old_address, old_size, new_size, flags);
+}
+#else
+
+#define MREMAP_MAYMOVE 1
+#define MREMAP_FIXED 2
+
+/*
+ * mremap wrapper for non-Linux systems not allowing MAYMOVE.
+ * This is not generic.
+*/
+static
+void *mremap_wrapper(void *old_address, size_t old_size,
+ size_t new_size, int flags)
+{
+ assert(!(flags & MREMAP_MAYMOVE));
+
+ return MAP_FAILED;
+}
+#endif
+
+/* Sleep delay in ms */
+#define RCU_SLEEP_DELAY_MS 10
+#define INIT_NR_THREADS 8
+#define ARENA_INIT_ALLOC \
+ sizeof(struct registry_chunk) \
+ + INIT_NR_THREADS * sizeof(struct rcu_reader)
+
+/*
+ * Active attempts to check for reader Q.S. before calling sleep().
+ */
+#define RCU_QS_ACTIVE_ATTEMPTS 100
+
+static
+int rcu_bp_refcount;
+
+/* If the headers do not support membarrier system call, fall back smp_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),
+};
+
+static
+void __attribute__((constructor)) rcu_bp_init(void);
+static
+void __attribute__((destructor)) rcu_bp_exit(void);
+
+int urcu_bp_has_sys_membarrier;
+
+/*
+ * 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;
+
+static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
+static int initialized;
+
+static pthread_key_t urcu_bp_key;
+
+struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
+
+/*
+ * Pointer to registry elements. 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);
+
+struct registry_chunk {
+ size_t data_len; /* data length */
+ size_t used; /* amount of data used */
+ struct cds_list_head node; /* chunk_list node */
+ char data[];
+};
+
+struct registry_arena {
+ struct cds_list_head chunk_list;
+};
+
+static struct registry_arena registry_arena = {
+ .chunk_list = CDS_LIST_HEAD_INIT(registry_arena.chunk_list),
+};
+
+/* Saved fork signal mask, protected by rcu_gp_lock */
+static sigset_t saved_fork_signal_mask;
+
+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);
+ 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);
+}
+
+static void smp_mb_master(void)
+{
+ if (caa_likely(urcu_bp_has_sys_membarrier))
+ (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
+ else
+ cmm_smp_mb();
+}
+
+/*
+ * 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;
+
+ /*
+ * 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++;
+
+ 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;
+ }
+ }
+
+ if (cds_list_empty(input_readers)) {
+ break;
+ } else {
+ /* Temporarily unlock the registry lock. */
+ mutex_unlock(&rcu_registry_lock);
+ if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
+ (void) poll(NULL, 0, RCU_SLEEP_DELAY_MS);
+ else
+ caa_cpu_relax();
+ /* Re-lock the registry lock before the next loop. */
+ mutex_lock(&rcu_registry_lock);
+ }
+ }
+}
+
+void synchronize_rcu(void)
+{
+ CDS_LIST_HEAD(cur_snap_readers);
+ CDS_LIST_HEAD(qsreaders);
+ sigset_t newmask, oldmask;
+ int ret;
+
+ ret = sigfillset(&newmask);
+ assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ assert(!ret);
+
+ mutex_lock(&rcu_gp_lock);
+
+ 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. */
+ /* 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);
+
+ /*
+ * 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 qparity update to memory before waiting for other parity
+ * quiescent state. Failure to do so could result in the writer waiting
+ * forever while new readers are always accessing data (no progress).
+ * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
+ */
+
+ /*
+ * 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.
+ */
+ smp_mb_master();
+out:
+ mutex_unlock(&rcu_registry_lock);
+ mutex_unlock(&rcu_gp_lock);
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ assert(!ret);
+}
+
+/*
+ * 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();
+}
+
+/*
+ * Only grow for now. If empty, allocate a ARENA_INIT_ALLOC sized chunk.
+ * Else, try expanding the last chunk. If this fails, allocate a new
+ * chunk twice as big as the last chunk.
+ * Memory used by chunks _never_ moves. A chunk could theoretically be
+ * freed when all "used" slots are released, but we don't do it at this
+ * point.
+ */
+static
+void expand_arena(struct registry_arena *arena)
+{
+ struct registry_chunk *new_chunk, *last_chunk;
+ size_t old_chunk_len, new_chunk_len;
+
+ /* No chunk. */
+ if (cds_list_empty(&arena->chunk_list)) {
+ assert(ARENA_INIT_ALLOC >=
+ sizeof(struct registry_chunk)
+ + sizeof(struct rcu_reader));
+ new_chunk_len = ARENA_INIT_ALLOC;
+ new_chunk = mmap(NULL, new_chunk_len,
+ PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE,
+ -1, 0);
+ if (new_chunk == MAP_FAILED)
+ abort();
+ memset(new_chunk, 0, new_chunk_len);
+ new_chunk->data_len =
+ new_chunk_len - sizeof(struct registry_chunk);
+ cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
+ return; /* We're done. */
+ }
+
+ /* Try expanding last chunk. */
+ last_chunk = cds_list_entry(arena->chunk_list.prev,
+ struct registry_chunk, node);
+ old_chunk_len =
+ last_chunk->data_len + sizeof(struct registry_chunk);
+ new_chunk_len = old_chunk_len << 1;
+
+ /* Don't allow memory mapping to move, just expand. */
+ new_chunk = mremap_wrapper(last_chunk, old_chunk_len,
+ new_chunk_len, 0);
+ if (new_chunk != MAP_FAILED) {
+ /* Should not have moved. */
+ assert(new_chunk == last_chunk);
+ memset((char *) last_chunk + old_chunk_len, 0,
+ new_chunk_len - old_chunk_len);
+ last_chunk->data_len =
+ new_chunk_len - sizeof(struct registry_chunk);
+ return; /* We're done. */
+ }
+
+ /* Remap did not succeed, we need to add a new chunk. */
+ new_chunk = mmap(NULL, new_chunk_len,
+ PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE,
+ -1, 0);
+ if (new_chunk == MAP_FAILED)
+ abort();
+ memset(new_chunk, 0, new_chunk_len);
+ new_chunk->data_len =
+ new_chunk_len - sizeof(struct registry_chunk);
+ cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
+}
+
+static
+struct rcu_reader *arena_alloc(struct registry_arena *arena)
+{
+ struct registry_chunk *chunk;
+ struct rcu_reader *rcu_reader_reg;
+ int expand_done = 0; /* Only allow to expand once per alloc */
+ size_t len = sizeof(struct rcu_reader);
+
+retry:
+ cds_list_for_each_entry(chunk, &arena->chunk_list, node) {
+ if (chunk->data_len - chunk->used < len)
+ continue;
+ /* Find spot */
+ for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
+ rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
+ rcu_reader_reg++) {
+ if (!rcu_reader_reg->alloc) {
+ rcu_reader_reg->alloc = 1;
+ chunk->used += len;
+ return rcu_reader_reg;
+ }
+ }
+ }
+
+ if (!expand_done) {
+ expand_arena(arena);
+ expand_done = 1;
+ goto retry;
+ }
+
+ return NULL;
+}
+
+/* Called with signals off and mutex locked */
+static
+void add_thread(void)
+{
+ struct rcu_reader *rcu_reader_reg;
+ int ret;
+
+ rcu_reader_reg = arena_alloc(®istry_arena);
+ if (!rcu_reader_reg)
+ abort();
+ ret = pthread_setspecific(urcu_bp_key, rcu_reader_reg);
+ if (ret)
+ abort();
+
+ /* Add to registry */
+ rcu_reader_reg->tid = pthread_self();
+ assert(rcu_reader_reg->ctr == 0);
+ cds_list_add(&rcu_reader_reg->node, ®istry);
+ /*
+ * Reader threads are pointing to the reader registry. This is
+ * why its memory should never be relocated.
+ */
+ URCU_TLS(rcu_reader) = rcu_reader_reg;
+}
+
+/* Called with mutex locked */
+static
+void cleanup_thread(struct registry_chunk *chunk,
+ struct rcu_reader *rcu_reader_reg)
+{
+ rcu_reader_reg->ctr = 0;
+ cds_list_del(&rcu_reader_reg->node);
+ rcu_reader_reg->tid = 0;
+ rcu_reader_reg->alloc = 0;
+ chunk->used -= sizeof(struct rcu_reader);
+}
+
+static
+struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
+{
+ struct registry_chunk *chunk;
+
+ cds_list_for_each_entry(chunk, ®istry_arena.chunk_list, node) {
+ if (rcu_reader_reg < (struct rcu_reader *) &chunk->data[0])
+ continue;
+ if (rcu_reader_reg >= (struct rcu_reader *) &chunk->data[chunk->data_len])
+ continue;
+ return chunk;
+ }
+ return NULL;
+}
+
+/* Called with signals off and mutex locked */
+static
+void remove_thread(struct rcu_reader *rcu_reader_reg)
+{
+ cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
+ URCU_TLS(rcu_reader) = NULL;
+}
+
+/* Disable signals, take mutex, add to registry */
+void rcu_bp_register(void)
+{
+ sigset_t newmask, oldmask;
+ int ret;
+
+ ret = sigfillset(&newmask);
+ if (ret)
+ abort();
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ if (ret)
+ abort();
+
+ /*
+ * Check if a signal concurrently registered our thread since
+ * the check in rcu_read_lock().
+ */
+ if (URCU_TLS(rcu_reader))
+ goto end;
+
+ /*
+ * Take care of early registration before urcu_bp constructor.
+ */
+ rcu_bp_init();
+
+ mutex_lock(&rcu_registry_lock);
+ add_thread();
+ mutex_unlock(&rcu_registry_lock);
+end:
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ if (ret)
+ abort();
+}
+
+/* Disable signals, take mutex, remove from registry */
+static
+void rcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
+{
+ sigset_t newmask, oldmask;
+ int ret;
+
+ ret = sigfillset(&newmask);
+ if (ret)
+ abort();
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ if (ret)
+ abort();
+
+ mutex_lock(&rcu_registry_lock);
+ remove_thread(rcu_reader_reg);
+ mutex_unlock(&rcu_registry_lock);
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ if (ret)
+ abort();
+ rcu_bp_exit();
+}
+
+/*
+ * Remove thread from the registry when it exits, and flag it as
+ * destroyed so garbage collection can take care of it.
+ */
+static
+void urcu_bp_thread_exit_notifier(void *rcu_key)
+{
+ rcu_bp_unregister(rcu_key);
+}
+
+static
+void rcu_bp_init(void)
+{
+ mutex_lock(&init_lock);
+ if (!rcu_bp_refcount++) {
+ int ret;
+
+ ret = pthread_key_create(&urcu_bp_key,
+ urcu_bp_thread_exit_notifier);
+ if (ret)
+ abort();
+ ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
+ if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
+ urcu_bp_has_sys_membarrier = 1;
+ }
+ initialized = 1;
+ }
+ mutex_unlock(&init_lock);
+}
+
+static
+void rcu_bp_exit(void)
+{
+ mutex_lock(&init_lock);
+ if (!--rcu_bp_refcount) {
+ struct registry_chunk *chunk, *tmp;
+ int ret;
+
+ cds_list_for_each_entry_safe(chunk, tmp,
+ ®istry_arena.chunk_list, node) {
+ munmap(chunk, chunk->data_len
+ + sizeof(struct registry_chunk));
+ }
+ CDS_INIT_LIST_HEAD(®istry_arena.chunk_list);
+ ret = pthread_key_delete(urcu_bp_key);
+ if (ret)
+ abort();
+ }
+ mutex_unlock(&init_lock);
+}
+
+/*
+ * Holding the rcu_gp_lock and rcu_registry_lock across fork will make
+ * sure we fork() don't race with a concurrent thread executing with
+ * any of those locks held. This ensures that the registry and data
+ * protected by rcu_gp_lock are in a coherent state in the child.
+ */
+void rcu_bp_before_fork(void)
+{
+ sigset_t newmask, oldmask;
+ int ret;
+
+ ret = sigfillset(&newmask);
+ assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ assert(!ret);
+ mutex_lock(&rcu_gp_lock);
+ mutex_lock(&rcu_registry_lock);
+ saved_fork_signal_mask = oldmask;
+}
+
+void rcu_bp_after_fork_parent(void)
+{
+ sigset_t oldmask;
+ int ret;
+
+ oldmask = saved_fork_signal_mask;
+ mutex_unlock(&rcu_registry_lock);
+ mutex_unlock(&rcu_gp_lock);
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ assert(!ret);
+}
+
+/*
+ * Prune all entries from registry except our own thread. Fits the Linux
+ * fork behavior. Called with rcu_gp_lock and rcu_registry_lock held.
+ */
+static
+void urcu_bp_prune_registry(void)
+{
+ struct registry_chunk *chunk;
+ struct rcu_reader *rcu_reader_reg;
+
+ cds_list_for_each_entry(chunk, ®istry_arena.chunk_list, node) {
+ for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
+ rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
+ rcu_reader_reg++) {
+ if (!rcu_reader_reg->alloc)
+ continue;
+ if (rcu_reader_reg->tid == pthread_self())
+ continue;
+ cleanup_thread(chunk, rcu_reader_reg);
+ }
+ }
+}
+
+void rcu_bp_after_fork_child(void)
+{
+ sigset_t oldmask;
+ int ret;
+
+ urcu_bp_prune_registry();
+ oldmask = saved_fork_signal_mask;
+ mutex_unlock(&rcu_registry_lock);
+ mutex_unlock(&rcu_gp_lock);
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+ assert(!ret);
+}
+
+void *rcu_dereference_sym_bp(void *p)
+{
+ return _rcu_dereference(p);
+}
+
+void *rcu_set_pointer_sym_bp(void **p, void *v)
+{
+ cmm_wmb();
+ uatomic_set(p, v);
+ return v;
+}
+
+void *rcu_xchg_pointer_sym_bp(void **p, void *v)
+{
+ cmm_wmb();
+ return uatomic_xchg(p, v);
+}
+
+void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
+{
+ cmm_wmb();
+ return uatomic_cmpxchg(p, old, _new);
+}
+
+DEFINE_RCU_FLAVOR(rcu_flavor);
+
+#include "urcu-call-rcu-impl.h"
+#include "urcu-defer-impl.h"
projects / userspace-rcu.git / blobdiff