From: Mathieu Desnoyers Date: Tue, 1 Oct 2013 14:51:10 +0000 (-0400) Subject: Fix urcu-bp: don't move registry X-Git-Tag: v0.8.1~8 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=a0d529ecc9949d776800f5a006974d6bf410910e;p=userspace-rcu.git Fix urcu-bp: don't move registry It is not correct to move the registry address range, since there are external references from reader threads. This will trigger on workloads with many threads. Typically, on Linux, mremap can expand the existing range, which is OK. However, if there is not enough space around the existing range, it may try to map it at a different address, which is incorrect. It is more likely that this bug will be observed on operating systems where urcu uses the mmap/munmap fallback instead of mremap. Moreover, prior to commit: "Fix: urcu-bp: Bulletproof RCU arena resize bug" this issue was hidden by the fact that each thread ended up with their own memory mapping (leaked), on Linux at least. Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu-bp.c b/urcu-bp.c index 93d781f..190a569 100644 --- a/urcu-bp.c +++ b/urcu-bp.c @@ -66,34 +66,25 @@ void *mremap_wrapper(void *old_address, size_t old_size, #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 +#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(). @@ -119,13 +110,20 @@ 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; /* 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; @@ -301,91 +299,150 @@ int rcu_read_ongoing(void) } /* - * 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_p; - size_t old_len; - - old_len = arena->len; - - if (!arena->p) - new_p = mmap(arena->p, len, + 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); - else - new_p = mremap_wrapper(arena->p, old_len, - len, MREMAP_MAYMOVE); - assert(new_p != MAP_FAILED); + 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. */ + } - /* - * Zero the newly allocated memory. Since mmap() does not - * clearly specify if memory is zeroed or not (although it is - * very likely that it is), be extra careful by not expecting - * the new range to be zeroed by mremap. - */ - bzero(new_p + old_len, len - old_len); + /* 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. */ + } - /* - * If we did not re-use the same region, we need to update the - * arena pointer. - */ - if (new_p != arena->p) - arena->p = new_p; + /* 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); +} - arena->len = len; +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) +static +void add_thread(void) { struct rcu_reader *rcu_reader_reg; - 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(); /* 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) { + struct registry_chunk *chunk; struct rcu_reader *rcu_reader_reg; - pthread_t tid; - int ret; - 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) - 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); + 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++) { + pthread_t tid; + int ret; + + if (!rcu_reader_reg->alloc) + 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; + chunk->used -= sizeof(struct rcu_reader); + } + } } } @@ -417,8 +474,12 @@ end: void rcu_bp_exit(void) { - if (registry_arena.p) - munmap(registry_arena.p, registry_arena.len); + struct registry_chunk *chunk, *tmp; + + cds_list_for_each_entry_safe(chunk, tmp, + ®istry_arena.chunk_list, node) { + munmap(chunk, chunk->data_len + sizeof(struct registry_chunk)); + } } /*