From 30a359d633f2eebf28f3e464e53b00befffbe86f Mon Sep 17 00:00:00 2001 From: Bas Nieuwenhuizen Date: Sat, 7 Aug 2021 23:31:00 +0200 Subject: [PATCH] util/fossilize_db: Add extra flock mutex. The flock is per-fd, not per thread, and we do it outside of the main mutex. This was done to avoid having to wait in the mutex, but we can get a case where one ends up running the body with the flock unlocked. Fix this by adding a mutex that doesn't need to be locked for reads. Fixes: 4f0f8133a35 "util/fossilize_db: Do not lock the fossilize db permanently." Reviewed-by: Timothy Arceri Part-of: --- src/util/fossilize_db.c | 12 +++++++++++- src/util/fossilize_db.h | 1 + 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/src/util/fossilize_db.c b/src/util/fossilize_db.c index 013575a67a1..e1709a1ff64 100644 --- a/src/util/fossilize_db.c +++ b/src/util/fossilize_db.c @@ -286,6 +286,7 @@ foz_prepare(struct foz_db *foz_db, char *cache_path) return false; simple_mtx_init(&foz_db->mtx, mtx_plain); + simple_mtx_init(&foz_db->flock_mtx, mtx_plain); foz_db->mem_ctx = ralloc_context(NULL); foz_db->index_db = _mesa_hash_table_u64_create(NULL); @@ -348,6 +349,7 @@ foz_destroy(struct foz_db *foz_db) if (foz_db->mem_ctx) { _mesa_hash_table_u64_destroy(foz_db->index_db); ralloc_free(foz_db->mem_ctx); + simple_mtx_destroy(&foz_db->flock_mtx); simple_mtx_destroy(&foz_db->mtx); } } @@ -434,7 +436,12 @@ foz_write_entry(struct foz_db *foz_db, const uint8_t *cache_key_160bit, if (!foz_db->alive) return false; - /* Wait for 1 second. This is done outside of the mutex as I believe there is more potential + /* The flock is per-fd, not per thread, we do it outside of the main mutex to avoid having to + * wait in the mutex potentially blocking reads. We use the secondary flock_mtx to stop race + * conditions between the write threads sharing the same file descriptor. */ + simple_mtx_lock(&foz_db->flock_mtx); + + /* Wait for 1 second. This is done outside of the main mutex as I believe there is more potential * for file contention than mtx contention of significant length. */ int err = lock_file_with_timeout(foz_db->file[0], 1000000000); if (err == -1) @@ -449,6 +456,7 @@ foz_write_entry(struct foz_db *foz_db, const uint8_t *cache_key_160bit, if (entry) { simple_mtx_unlock(&foz_db->mtx); flock(fileno(foz_db->file[0]), LOCK_UN); + simple_mtx_unlock(&foz_db->flock_mtx); return NULL; } @@ -511,6 +519,7 @@ foz_write_entry(struct foz_db *foz_db, const uint8_t *cache_key_160bit, simple_mtx_unlock(&foz_db->mtx); flock(fileno(foz_db->file[0]), LOCK_UN); + simple_mtx_unlock(&foz_db->flock_mtx); return true; @@ -518,6 +527,7 @@ fail: simple_mtx_unlock(&foz_db->mtx); fail_file: flock(fileno(foz_db->file[0]), LOCK_UN); + simple_mtx_unlock(&foz_db->flock_mtx); return false; } #else diff --git a/src/util/fossilize_db.h b/src/util/fossilize_db.h index 9b6d34122aa..e05aef9e4ca 100644 --- a/src/util/fossilize_db.h +++ b/src/util/fossilize_db.h @@ -76,6 +76,7 @@ struct foz_db { FILE *file[FOZ_MAX_DBS]; /* An array of all foz dbs */ FILE *db_idx; /* The default writable foz db idx */ simple_mtx_t mtx; /* Mutex for file/hash table read/writes */ + simple_mtx_t flock_mtx; /* Mutex for flocking the file for writes */ void *mem_ctx; struct hash_table_u64 *index_db; /* Hash table of all foz db entries */ bool alive;