sunrpc: never return expired entries in sunrpc_cache_lookup

If sunrpc_cache_lookup finds an expired entry, remove it from
the cache and return a freshly created non-VALID entry instead.
This ensures that we only ever get a usable entry, or an
entry that will become usable once an update arrives.
i.e. we will never need to repeat the lookup.

This allows us to remove the 'is_expired' test from cache_check
(i.e. from cache_is_valid).  cache_check should never get an expired
entry as 'lookup' will never return one.  If it does happen - due to
inconvenient timing - then just accept it as still valid, it won't be
very much past it's use-by date.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

1 files changed, 14 insertions, 3 deletions

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 9826c5ceb995..3e1ef8bf4dc2 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -59,7 +59,7 @@ struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
                                        struct cache_head *key, int hash)
 {
         struct cache_head **head,  **hp;
-        struct cache_head *new = NULL;
+        struct cache_head *new = NULL, *freeme = NULL;
 
         head = &detail->hash_table[hash];
 
@@ -68,6 +68,9 @@ struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
         for (hp=head; *hp != NULL ; hp = &(*hp)->next) {
                 struct cache_head *tmp = *hp;
                 if (detail->match(tmp, key)) {
+                        if (cache_is_expired(detail, tmp))
+                                /* This entry is expired, we will discard it. */
+                                break;
                         cache_get(tmp);
                         read_unlock(&detail->hash_lock);
                         return tmp;
@@ -92,6 +95,13 @@ struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
         for (hp=head; *hp != NULL ; hp = &(*hp)->next) {
                 struct cache_head *tmp = *hp;
                 if (detail->match(tmp, key)) {
+                        if (cache_is_expired(detail, tmp)) {
+                                *hp = tmp->next;
+                                tmp->next = NULL;
+                                detail->entries --;
+                                freeme = tmp;
+                                break;
+                        }
                         cache_get(tmp);
                         write_unlock(&detail->hash_lock);
                         cache_put(new, detail);
@@ -104,6 +114,8 @@ struct cache_head *sunrpc_cache_lookup(struct cache_detail *detail,
         cache_get(new);
         write_unlock(&detail->hash_lock);
 
+        if (freeme)
+                cache_put(freeme, detail);
         return new;
 }
 EXPORT_SYMBOL_GPL(sunrpc_cache_lookup);
@@ -189,8 +201,7 @@ static int cache_make_upcall(struct cache_detail *cd, struct cache_head *h)
 
 static inline int cache_is_valid(struct cache_detail *detail, struct cache_head *h)
 {
-        if (!test_bit(CACHE_VALID, &h->flags) ||
-            cache_is_expired(detail, h))
+        if (!test_bit(CACHE_VALID, &h->flags))
                 return -EAGAIN;
         else {
                 /* entry is valid */