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authorNeilBrown <neilb@suse.com>2019-03-22 05:16:56 +0300
committerJ. Bruce Fields <bfields@redhat.com>2019-04-24 16:46:34 +0300
commit9d69338c8c5fc68e9ae3ab23d01356ca024b789e (patch)
tree34af56ec88a155c230bee43fff7517fb5379c58a /net/sunrpc/cache.c
parent0ab88ca4bcf18ba21058d8f19220f60afe0d34d8 (diff)
downloadlinux-9d69338c8c5fc68e9ae3ab23d01356ca024b789e.tar.xz
sunrpc/cache: handle missing listeners better.
If no handler (such as rpc.mountd) has opened a cache 'channel', the sunrpc cache responds to all lookup requests with -ENOENT. This is particularly important for the auth.unix.gid cache which is optional. If the channel was open briefly and an upcall was written to it, this upcall remains pending even when the handler closes the channel. When an upcall is pending, the code currently doesn't check if there are still listeners, it only performs that check before sending an upcall. As the cache treads a recently closes channel (closed less than 30 seconds ago) as "potentially still open", there is a reasonable sized window when a request can become pending in a closed channel, and thereby block lookups indefinitely. This can easily be demonstrated by running cat /proc/net/rpc/auth.unix.gid/channel and then trying to mount an NFS filesystem from this host. It will block indefinitely (unless mountd is run with --manage-gids, or krb5 is used). When cache_check() finds that an upcall is pending, it should perform the "cache_listeners_exist()" exist test. If no listeners do exist, the request should be negated. With this change in place, there can still be a 30second wait on mount, until the cache gives up waiting for a handler to come back, but this is much better than an indefinite wait. Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net/sunrpc/cache.c')
-rw-r--r--net/sunrpc/cache.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 261131dfa1f1..d22328984853 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -40,6 +40,7 @@
static bool cache_defer_req(struct cache_req *req, struct cache_head *item);
static void cache_revisit_request(struct cache_head *item);
+static bool cache_listeners_exist(struct cache_detail *detail);
static void cache_init(struct cache_head *h, struct cache_detail *detail)
{
@@ -306,7 +307,8 @@ int cache_check(struct cache_detail *detail,
cache_fresh_unlocked(h, detail);
break;
}
- }
+ } else if (!cache_listeners_exist(detail))
+ rv = try_to_negate_entry(detail, h);
}
if (rv == -EAGAIN) {