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Don't truncate valid cachefiles

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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>
This commit is contained in:
Lars Hjemli 2006-12-11 22:53:50 +01:00
parent 44923f8953
commit fbaf1171b4
3 changed files with 16 additions and 4 deletions
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5
cache.c
View File

@ -99,6 +99,11 @@ int cache_unlock(struct cacheitem *item)
return (rename(fmt("%s.lock", item->name), item->name) == 0); 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) int cache_expired(struct cacheitem *item)
{ {
if (item->ttl < 0) if (item->ttl < 0)

10
cgit.c
View File

@ -61,13 +61,19 @@ static void cgit_check_cache(struct cacheitem *item)
sleep(1); sleep(1);
goto top; goto top;
} }
if (!cache_exist(item)) if (!cache_exist(item)) {
cgit_fill_cache(item); cgit_fill_cache(item);
cache_unlock(item); cache_unlock(item);
} else {
cache_cancel_lock(item);
}
} else if (cache_expired(item) && cache_lock(item)) { } else if (cache_expired(item) && cache_lock(item)) {
if (cache_expired(item)) if (cache_expired(item)) {
cgit_fill_cache(item); cgit_fill_cache(item);
cache_unlock(item); cache_unlock(item);
} else {
cache_cancel_lock(item);
}
} }
} }

1
cgit.h
View File

@ -66,6 +66,7 @@ extern int cgit_parse_query(char *txt, configfn fn);
extern void cache_prepare(struct cacheitem *item); extern void cache_prepare(struct cacheitem *item);
extern int cache_lock(struct cacheitem *item); extern int cache_lock(struct cacheitem *item);
extern int cache_unlock(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_exist(struct cacheitem *item);
extern int cache_expired(struct cacheitem *item); extern int cache_expired(struct cacheitem *item);