+++ /dev/null
-/*
- * SPDX-License-Identifier: LGPL-2.1-or-later
- *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
- *
- * Userspace RCU library for LTTng-UST, derived from liburcu "bulletproof" version.
- */
-
-#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 <stdbool.h>
-#include <sys/mman.h>
-
-#include <urcu/arch.h>
-#include <urcu/wfcqueue.h>
-#include <lttng/urcu/static/urcu-ust.h>
-#include <lttng/urcu/pointer.h>
-#include <urcu/tls-compat.h>
-
-/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
-#undef _LGPL_SOURCE
-#include <lttng/urcu/urcu-ust.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 lttng_ust_urcu_reader)
-
-/*
- * Active attempts to check for reader Q.S. before calling sleep().
- */
-#define RCU_QS_ACTIVE_ATTEMPTS 100
-
-static
-int lttng_ust_urcu_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),
- /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
- /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
- MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
- MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
-};
-
-static
-void _lttng_ust_urcu_init(void)
- __attribute__((constructor));
-static
-void lttng_ust_urcu_exit(void)
- __attribute__((destructor));
-
-#ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
-int lttng_ust_urcu_has_sys_membarrier;
-#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;
-
-static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
-static int initialized;
-
-static pthread_key_t lttng_ust_urcu_key;
-
-struct lttng_ust_urcu_gp lttng_ust_urcu_gp = { .ctr = LTTNG_UST_URCU_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 lttng_ust_urcu_reader *, lttng_ust_urcu_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)
- abort();
-#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
- while ((ret = pthread_mutex_trylock(mutex)) != 0) {
- if (ret != EBUSY && ret != EINTR)
- abort();
- 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)
- abort();
-}
-
-static void smp_mb_master(void)
-{
- if (caa_likely(lttng_ust_urcu_has_sys_membarrier)) {
- if (membarrier(MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0))
- abort();
- } 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 lttng_ust_urcu_reader *index, *tmp;
-
- /*
- * Wait for each thread URCU_TLS(lttng_ust_urcu_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 (lttng_ust_urcu_reader_state(&index->ctr)) {
- case LTTNG_UST_URCU_READER_ACTIVE_CURRENT:
- if (cur_snap_readers) {
- cds_list_move(&index->node,
- cur_snap_readers);
- break;
- }
- /* Fall-through */
- case LTTNG_UST_URCU_READER_INACTIVE:
- cds_list_move(&index->node, qsreaders);
- break;
- case LTTNG_UST_URCU_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 lttng_ust_urcu_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(lttng_ust_urcu_gp.ctr, lttng_ust_urcu_gp.ctr ^ LTTNG_UST_URCU_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 lttng_ust_urcu_read_lock(void)
-{
- _lttng_ust_urcu_read_lock();
-}
-
-void lttng_ust_urcu_read_unlock(void)
-{
- _lttng_ust_urcu_read_unlock();
-}
-
-int lttng_ust_urcu_read_ongoing(void)
-{
- return _lttng_ust_urcu_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 lttng_ust_urcu_reader));
- new_chunk_len = ARENA_INIT_ALLOC;
- new_chunk = (struct registry_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 = (struct registry_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 lttng_ust_urcu_reader *arena_alloc(struct registry_arena *arena)
-{
- struct registry_chunk *chunk;
- struct lttng_ust_urcu_reader *rcu_reader_reg;
- int expand_done = 0; /* Only allow to expand once per alloc */
- size_t len = sizeof(struct lttng_ust_urcu_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 lttng_ust_urcu_reader *) &chunk->data[0];
- rcu_reader_reg < (struct lttng_ust_urcu_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 lttng_ust_urcu_reader *rcu_reader_reg;
- int ret;
-
- rcu_reader_reg = arena_alloc(®istry_arena);
- if (!rcu_reader_reg)
- abort();
- ret = pthread_setspecific(lttng_ust_urcu_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(lttng_ust_urcu_reader) = rcu_reader_reg;
-}
-
-/* Called with mutex locked */
-static
-void cleanup_thread(struct registry_chunk *chunk,
- struct lttng_ust_urcu_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 lttng_ust_urcu_reader);
-}
-
-static
-struct registry_chunk *find_chunk(struct lttng_ust_urcu_reader *rcu_reader_reg)
-{
- struct registry_chunk *chunk;
-
- cds_list_for_each_entry(chunk, ®istry_arena.chunk_list, node) {
- if (rcu_reader_reg < (struct lttng_ust_urcu_reader *) &chunk->data[0])
- continue;
- if (rcu_reader_reg >= (struct lttng_ust_urcu_reader *) &chunk->data[chunk->data_len])
- continue;
- return chunk;
- }
- return NULL;
-}
-
-/* Called with signals off and mutex locked */
-static
-void remove_thread(struct lttng_ust_urcu_reader *rcu_reader_reg)
-{
- cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
- URCU_TLS(lttng_ust_urcu_reader) = NULL;
-}
-
-/* Disable signals, take mutex, add to registry */
-void lttng_ust_urcu_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(lttng_ust_urcu_reader))
- goto end;
-
- /*
- * Take care of early registration before lttng_ust_urcu constructor.
- */
- _lttng_ust_urcu_init();
-
- mutex_lock(&rcu_registry_lock);
- add_thread();
- mutex_unlock(&rcu_registry_lock);
-end:
- ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
- if (ret)
- abort();
-}
-
-void lttng_ust_urcu_register_thread(void)
-{
- if (caa_unlikely(!URCU_TLS(lttng_ust_urcu_reader)))
- lttng_ust_urcu_register(); /* If not yet registered. */
-}
-
-/* Disable signals, take mutex, remove from registry */
-static
-void lttng_ust_urcu_unregister(struct lttng_ust_urcu_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();
- lttng_ust_urcu_exit();
-}
-
-/*
- * Remove thread from the registry when it exits, and flag it as
- * destroyed so garbage collection can take care of it.
- */
-static
-void lttng_ust_urcu_thread_exit_notifier(void *rcu_key)
-{
- lttng_ust_urcu_unregister(rcu_key);
-}
-
-#ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
-static
-void lttng_ust_urcu_sys_membarrier_status(bool available)
-{
- if (!available)
- abort();
-}
-#else
-static
-void lttng_ust_urcu_sys_membarrier_status(bool available)
-{
- if (!available)
- return;
- lttng_ust_urcu_has_sys_membarrier = 1;
-}
-#endif
-
-static
-void lttng_ust_urcu_sys_membarrier_init(void)
-{
- bool available = false;
- int mask;
-
- mask = membarrier(MEMBARRIER_CMD_QUERY, 0);
- if (mask >= 0) {
- if (mask & MEMBARRIER_CMD_PRIVATE_EXPEDITED) {
- if (membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0))
- abort();
- available = true;
- }
- }
- lttng_ust_urcu_sys_membarrier_status(available);
-}
-
-static
-void _lttng_ust_urcu_init(void)
-{
- mutex_lock(&init_lock);
- if (!lttng_ust_urcu_refcount++) {
- int ret;
-
- ret = pthread_key_create(<tng_ust_urcu_key,
- lttng_ust_urcu_thread_exit_notifier);
- if (ret)
- abort();
- lttng_ust_urcu_sys_membarrier_init();
- initialized = 1;
- }
- mutex_unlock(&init_lock);
-}
-
-static
-void lttng_ust_urcu_exit(void)
-{
- mutex_lock(&init_lock);
- if (!--lttng_ust_urcu_refcount) {
- struct registry_chunk *chunk, *tmp;
- int ret;
-
- cds_list_for_each_entry_safe(chunk, tmp,
- ®istry_arena.chunk_list, node) {
- munmap((void *) chunk, chunk->data_len
- + sizeof(struct registry_chunk));
- }
- CDS_INIT_LIST_HEAD(®istry_arena.chunk_list);
- ret = pthread_key_delete(lttng_ust_urcu_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 lttng_ust_urcu_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 lttng_ust_urcu_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 lttng_ust_urcu_prune_registry(void)
-{
- struct registry_chunk *chunk;
- struct lttng_ust_urcu_reader *rcu_reader_reg;
-
- cds_list_for_each_entry(chunk, ®istry_arena.chunk_list, node) {
- for (rcu_reader_reg = (struct lttng_ust_urcu_reader *) &chunk->data[0];
- rcu_reader_reg < (struct lttng_ust_urcu_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 lttng_ust_urcu_after_fork_child(void)
-{
- sigset_t oldmask;
- int ret;
-
- lttng_ust_urcu_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 / lttng-ust.git / blobdiff