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authorLars Hjemli <hjemli@gmail.com>2006-12-11 22:53:50 +0100
committerLars Hjemli <hjemli@gmail.com>2006-12-11 22:53:50 +0100
commitfbaf1171b4e343929dd43ecac7cd9d1c692b84ec (patch)
tree40b7007b2e1e85f2e91e052b33555df2e9fb5e14
parent44923f8953c66dc9b852316b655ab3b5aec9478e (diff)
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>
-rw-r--r--cache.c5
-rw-r--r--cgit.c14
-rw-r--r--cgit.h1
3 files changed, 16 insertions, 4 deletions
diff --git a/cache.c b/cache.c
index 2e1ef8c..b947a34 100644
--- 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 d1abaa0..0f72f2d 100644
--- 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 c1dcc97..c9554a7 100644
--- 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);