[PATCH 3.16 22/99] sunrpc: fix cache_head leak due to queued request

[Ben Hutchings]

3.16.65-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Vasily Averin <vvs@xxxxxxxxxxxxx>

commit 4ecd55ea074217473f94cfee21bb72864d39f8d7 upstream.

After commit d202cce8963d, an expired cache_head can be removed from the
cache_detail's hash.

However, the expired cache_head may be waiting for a reply from a
previously submitted request. Such a cache_head has an increased
refcounter and therefore it won't be freed after cache_put(freeme).

Because the cache_head was removed from the hash it cannot be found
during cache_clean() and can be leaked forever, together with stalled
cache_request and other taken resources.

In our case we noticed it because an entry in the export cache was
holding a reference on a filesystem.

Fixes d202cce8963d ("sunrpc: never return expired entries in sunrpc_cache_lookup")
Cc: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx>
Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Reviewed-by: NeilBrown <neilb@xxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
[bwh: Backported to 3.16:
 - cache_fresh_lock() doesn't take a struct cache_detail pointer
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/sunrpc/cache.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -50,6 +50,10 @@ static void cache_init(struct cache_head
 	h->last_refresh = now;
 }
 
+static void cache_fresh_locked(struct cache_head *head, time_t expiry);
+static void cache_fresh_unlocked(struct cache_head *head,
+				struct cache_detail *detail);
+
 struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
 				       struct cache_head *key, int hash)
 {
@@ -94,6 +98,7 @@ struct cache_head *sunrpc_cache_lookup(s
 				*hp = tmp->next;
 				tmp->next = NULL;
 				detail->entries --;
+				cache_fresh_locked(tmp, 0);
 				freeme = tmp;
 				break;
 			}
@@ -109,8 +114,10 @@ struct cache_head *sunrpc_cache_lookup(s
 	cache_get(new);
 	write_unlock(&detail->hash_lock);
 
-	if (freeme)
+	if (freeme) {
+		cache_fresh_unlocked(freeme, detail);
 		cache_put(freeme, detail);
+	}
 	return new;
 }
 EXPORT_SYMBOL_GPL(sunrpc_cache_lookup);