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[PATCH 4.20 10/65] sunrpc: fix cache_head leak due to queued request




4.20-stable 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>
Cc: stable@xxxxxxxxxx # 2.6.35
Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Reviewed-by: NeilBrown <neilb@xxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/sunrpc/cache.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -54,6 +54,11 @@ static void cache_init(struct cache_head
 	h->last_refresh = now;
 }
 
+static void cache_fresh_locked(struct cache_head *head, time_t expiry,
+				struct cache_detail *detail);
+static void cache_fresh_unlocked(struct cache_head *head,
+				struct cache_detail *detail);
+
 static struct cache_head *sunrpc_cache_find_rcu(struct cache_detail *detail,
 						struct cache_head *key,
 						int hash)
@@ -100,6 +105,7 @@ static struct cache_head *sunrpc_cache_a
 			if (cache_is_expired(detail, tmp)) {
 				hlist_del_init_rcu(&tmp->cache_list);
 				detail->entries --;
+				cache_fresh_locked(tmp, 0, detail);
 				freeme = tmp;
 				break;
 			}
@@ -115,8 +121,10 @@ static struct cache_head *sunrpc_cache_a
 	cache_get(new);
 	spin_unlock(&detail->hash_lock);
 
-	if (freeme)
+	if (freeme) {
+		cache_fresh_unlocked(freeme, detail);
 		cache_put(freeme, detail);
+	}
 	return new;
 }