#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"
#define MREMAP_FIXED 2
/*
- * mremap wrapper for non-Linux systems. Maps a RW, anonymous private mapping.
+ * 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)
{
- void *new_address;
-
- assert(flags & MREMAP_MAYMOVE);
- assert(!(flags & MREMAP_FIXED));
- new_address = mmap(old_address, new_size,
- PROT_READ | PROT_WRITE,
- MAP_ANONYMOUS | MAP_PRIVATE,
- -1, 0);
- if (new_address == MAP_FAILED)
- return MAP_FAILED;
- if (old_address) {
- memcpy(new_address, old_address, old_size);
- munmap(old_address, old_size);
- }
- return new_address;
+ assert(!(flags & MREMAP_MAYMOVE));
+
+ return MAP_FAILED;
}
#endif
-/* Sleep delay in us */
-#define RCU_SLEEP_DELAY 1000
-#define ARENA_INIT_ALLOC 16
+/* 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
-void __attribute__((destructor)) rcu_bp_exit(void);
-
-static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
+static
+int rcu_bp_refcount;
-#ifdef DEBUG_YIELD
-unsigned int rcu_yield_active;
-DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
+/* 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;
/*
- * Global grace period counter.
- * Contains the current RCU_GP_CTR_PHASE.
- * 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.
+ * 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.
*/
-unsigned long rcu_gp_ctr = RCU_GP_COUNT;
+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
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 {
- void *p;
- size_t len;
- size_t used;
+ struct cds_list_head chunk_list;
};
-static struct registry_arena registry_arena;
+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 rcu_gc_registry(void);
-
static void mutex_lock(pthread_mutex_t *mutex)
{
int 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)
{
- int wait_loops = 0;
+ 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.
+ * rcu_gp.ctr value.
*/
for (;;) {
- wait_loops++;
+ 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 (cds_list_empty(input_readers)) {
break;
} else {
- if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
- usleep(RCU_SLEEP_DELAY);
+ /* 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);
}
}
}
sigset_t newmask, oldmask;
int ret;
- ret = sigemptyset(&newmask);
+ ret = sigfillset(&newmask);
assert(!ret);
- ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
+ 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 */
- cmm_smp_mb();
-
- /* Remove old registry elements */
- rcu_gc_registry();
+ 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);
cmm_smp_mb();
/* Switch parity: 0 -> 1, 1 -> 0 */
- CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+ CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
/*
* Must commit qparity update to memory before waiting for other parity
/*
* 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);
* Finish waiting for reader threads before letting the old ptr being
* freed.
*/
- cmm_smp_mb();
+ smp_mb_master();
out:
+ mutex_unlock(&rcu_registry_lock);
mutex_unlock(&rcu_gp_lock);
ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
assert(!ret);
}
/*
- * only grow for now.
+ * 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 resize_arena(struct registry_arena *arena, size_t len)
+static
+void expand_arena(struct registry_arena *arena)
{
- void *new_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. */
+ }
- if (!arena->p)
- new_arena = mmap(arena->p, len,
- PROT_READ | PROT_WRITE,
- MAP_ANONYMOUS | MAP_PRIVATE,
- -1, 0);
- else
- new_arena = mremap_wrapper(arena->p, arena->len,
- len, MREMAP_MAYMOVE);
- assert(new_arena != MAP_FAILED);
+ /* 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. */
+ }
- /*
- * re-used the same region ?
- */
- if (new_arena == arena->p)
- return;
+ /* 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);
- bzero(new_arena + arena->len, len - arena->len);
- arena->p = new_arena;
+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)
+static
+void add_thread(void)
{
struct rcu_reader *rcu_reader_reg;
+ int ret;
- if (registry_arena.len
- < registry_arena.used + sizeof(struct rcu_reader))
- resize_arena(®istry_arena,
- caa_max(registry_arena.len << 1, ARENA_INIT_ALLOC));
- /*
- * Find a free spot.
- */
- for (rcu_reader_reg = registry_arena.p;
- (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
- rcu_reader_reg++) {
- if (!rcu_reader_reg->alloc)
- break;
- }
- rcu_reader_reg->alloc = 1;
- registry_arena.used += sizeof(struct rcu_reader);
+ 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 signals off and mutex locked */
-static void rcu_gc_registry(void)
+/* Called with mutex locked */
+static
+void cleanup_thread(struct registry_chunk *chunk,
+ struct rcu_reader *rcu_reader_reg)
{
- struct rcu_reader *rcu_reader_reg;
- pthread_t tid;
- int ret;
+ 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);
+}
- for (rcu_reader_reg = registry_arena.p;
- (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
- rcu_reader_reg++) {
- if (!rcu_reader_reg->alloc)
+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;
- tid = rcu_reader_reg->tid;
- ret = pthread_kill(tid, 0);
- assert(ret != EINVAL);
- if (ret == ESRCH) {
- cds_list_del(&rcu_reader_reg->node);
- rcu_reader_reg->ctr = 0;
- rcu_reader_reg->alloc = 0;
- registry_arena.used -= sizeof(struct rcu_reader);
- }
+ 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 */
sigset_t newmask, oldmask;
int ret;
- ret = sigemptyset(&newmask);
- assert(!ret);
- ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
- assert(!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(). */
+ * the check in rcu_read_lock().
+ */
if (URCU_TLS(rcu_reader))
goto end;
- mutex_lock(&rcu_gp_lock);
+ /*
+ * Take care of early registration before urcu_bp constructor.
+ */
+ rcu_bp_init();
+
+ mutex_lock(&rcu_registry_lock);
add_thread();
- mutex_unlock(&rcu_gp_lock);
+ mutex_unlock(&rcu_registry_lock);
end:
ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
- assert(!ret);
+ 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)
{
- if (registry_arena.p)
- munmap(registry_arena.p, registry_arena.len);
+ 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 across fork will make sure we fork() don't race with
- * a concurrent thread executing with this same lock held. This ensures that the
- * registry is in a coherent state in the child.
+ * 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 = sigemptyset(&newmask);
+ ret = sigfillset(&newmask);
assert(!ret);
- ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
assert(!ret);
mutex_lock(&rcu_gp_lock);
+ mutex_lock(&rcu_registry_lock);
saved_fork_signal_mask = 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;
- rcu_gc_registry();
+ 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);
projects / urcu.git / blobdiff