Author: Lars Hjemli <hjemli@gmail.com>
Avoid infinite loops in caching layer Add a global variable, cgit_max_lock_attemps, to avoid the possibility of infinite loops when failing to acquire a lockfile. This could happen on broken setups or under crazy server load. Incidentally, this also fixes a lurking bug in cache_lock() where an uninitialized returnvalue was used. Signed-off-by: Lars Hjemli <hjemli@gmail.com>
cache.c | 35 ++++++++++++++++++++++------------- cgit.c | 9 ++++++++- cgit.h | 1 +
diff --git a/cache.c b/cache.c index 0ffa502c119ae33deaac913eabb742679cf4fe18..2e1ef8cc9e0fe7742965a1b3e845f12fa1fab13f 100644 --- a/cache.c +++ b/cache.c @@ -61,26 +61,35 @@ } return 1; } +int cache_refill_overdue(const char *lockfile) +{ + struct stat st; + + if (stat(lockfile, &st)) + return 0; + else + return (time(NULL) - st.st_mtime > cgit_cache_max_create_time); +} + int cache_lock(struct cacheitem *item) { - int ret; + int i = 0; char *lockfile = fmt("%s.lock", item->name); - top: - item->fd = open(lockfile, O_WRONLY | O_CREAT | O_EXCL, S_IRUSR|S_IWUSR); + top: + if (++i > cgit_max_lock_attempts) + die("cache_lock: unable to lock %s: %s", + item->name, strerror(errno)); + + item->fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR); + if (item->fd == NOLOCK && errno == ENOENT && cache_create_dirs()) goto top; - if (item->fd == NOLOCK && errno == EEXIST) { - struct stat st; - time_t t; - if (stat(lockfile, &st)) - return ret; - t = time(NULL); - if (t-st.st_mtime > cgit_cache_max_create_time && - !unlink(lockfile)) + + if (item->fd == NOLOCK && errno == EEXIST && + cache_refill_overdue(lockfile) && !unlink(lockfile)) goto top; - return 0; - } + return (item->fd > 0); } diff --git a/cgit.c b/cgit.c index 7f14016fb70ecb380ffafaa3e7f9f8d92fb362c5..dc911257afdbc3350e69f124f2b725b656e912d3 100644 --- a/cgit.c +++ b/cgit.c @@ -31,6 +31,7 @@ char *cgit_virtual_root = NULL; char *cgit_cache_root = "/var/cache/cgit"; +int cgit_max_lock_attempts = 5; int cgit_cache_root_ttl = 5; int cgit_cache_repo_ttl = 5; int cgit_cache_dynamic_ttl = 5; @@ -465,11 +466,17 @@ } static void cgit_refresh_cache(struct cacheitem *item) { + int i = 0; + cache_prepare(item); top: + if (++i > cgit_max_lock_attempts) { + die("cgit_refresh_cache: unable to lock %s: %s", + item->name, strerror(errno)); + } if (!cache_exist(item)) { if (!cache_lock(item)) { - sched_yield(); + sleep(1); goto top; } if (!cache_exist(item)) diff --git a/cgit.h b/cgit.h index 3b0994a775492f652359ff45f7342c7787f9dc44..7e4bfeff219442d64d6876a77a8fa855c376b38c 100644 --- a/cgit.h +++ b/cgit.h @@ -23,6 +23,7 @@ extern char *cgit_logo_link; extern char *cgit_virtual_root; extern char *cgit_cache_root; +extern int cgit_max_lock_attempts; extern int cgit_cache_root_ttl; extern int cgit_cache_repo_ttl; extern int cgit_cache_dynamic_ttl;