[urcu.git] / urcu-bp.c

/*
 * 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 _GNU_SOURCE
#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(&registry))
                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(&registry, &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, &registry);

        /*
         * 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();
                bzero(new_chunk, 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);
                bzero((char *) last_chunk + old_chunk_len,
                        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();
        bzero(new_chunk, 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(&registry_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, &registry);
        /*
         * 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, &registry_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,
                                &registry_arena.chunk_list, node) {
                        munmap(chunk, chunk->data_len
                                        + sizeof(struct registry_chunk));
                }
                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, &registry_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"