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>

diff --git a/cache.c b/cache.c
index 2e1ef8cc9e0fe7742965a1b3e845f12fa1fab13f..b947a34e8046b9a5169700cd1205356aac2d4fa7 100644 (file)
--- a/cache.c
+++ b/cache.c
@@ -99,6 +99,11 @@ int cache_unlock(struct cacheitem *item)
        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 (file)
--- a/cgit.c
+++ b/cgit.c
@@ -61,13 +61,19 @@ static void cgit_check_cache(struct cacheitem *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 (file)
--- a/cgit.h
+++ b/cgit.h
@@ -66,6 +66,7 @@ extern int cgit_parse_query(char *txt, configfn fn);
 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);