Author: Lars Hjemli <hjemli@gmail.com>
Don't truncate valid cachefiles
An embarrassing thinko in cgit_check_cache() would truncate valid cachefiles
in the following situation:
1) process A notices a missing/expired cachefile
2) process B gets scheduled, locks, fills and unlocks the cachefile
3) process A gets scheduled, locks the cachefile, notices that the cachefile
now exist/is not expired anymore, and continues to overwrite it with an
empty lockfile.
Thanks to Linus for noticing (again).
Signed-off-by: Lars Hjemli <hjemli@gmail.com>
cache.c | 5 +++++ cgit.c | 14 ++++++++++---- cgit.h | 1 +
diff --git a/cache.c b/cache.c index 2e1ef8cc9e0fe7742965a1b3e845f12fa1fab13f..b947a34e8046b9a5169700cd1205356aac2d4fa7 100644 --- a/cache.c +++ b/cache.c @@ -99,6 +99,11 @@ close(item->fd); return (rename(fmt("%s.lock", item->name), item->name) == 0); } +int cache_cancel_lock(struct cacheitem *item) +{ + return (unlink(fmt("%s.lock", item->name)) == 0); +} + int cache_expired(struct cacheitem *item) { if (item->ttl < 0) diff --git a/cgit.c b/cgit.c index d1abaa052135a8be8f0a13c0ccb9e7c53c4c8347..0f72f2d67ba9e81c97da65d03552eff117794d18 100644 --- a/cgit.c +++ b/cgit.c @@ -61,13 +61,19 @@ if (!cache_lock(item)) { sleep(1); goto top; } - if (!cache_exist(item)) + if (!cache_exist(item)) { cgit_fill_cache(item); - cache_unlock(item); + cache_unlock(item); + } else { + cache_cancel_lock(item); + } } else if (cache_expired(item) && cache_lock(item)) { - if (cache_expired(item)) + if (cache_expired(item)) { cgit_fill_cache(item); - cache_unlock(item); + cache_unlock(item); + } else { + cache_cancel_lock(item); + } } } diff --git a/cgit.h b/cgit.h index c1dcc9716b743a608cf80163845cb73755682fec..c9554a7ae759d5748df6570250e74232271944be 100644 --- a/cgit.h +++ b/cgit.h @@ -66,6 +66,7 @@ extern void cache_prepare(struct cacheitem *item); extern int cache_lock(struct cacheitem *item); extern int cache_unlock(struct cacheitem *item); +extern int cache_cancel_lock(struct cacheitem *item); extern int cache_exist(struct cacheitem *item); extern int cache_expired(struct cacheitem *item);