nfsd4: fix hang on fast-booting nfs servers

The last_close field of a cache_detail is initialized to zero, so the
condition

	detail->last_close < seconds_since_boot() - 30

may be false even for a cache that was never opened.

However, we want to immediately fail upcalls to caches that were never
opened: in the case of the auth_unix_gid cache, especially, which may
never be opened by mountd (if the --manage-gids option is not set), we
want to fail the upcall immediately.  Otherwise client requests will be
dropped unnecessarily on reboot.

Also document these conditions.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 20 insertions, 4 deletions

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index da872f9fe1e0..ca7c621cd975 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1091,6 +1091,23 @@ static void warn_no_listener(struct cache_detail *detail)
         }
 }
 
+static bool cache_listeners_exist(struct cache_detail *detail)
+{
+        if (atomic_read(&detail->readers))
+                return true;
+        if (detail->last_close == 0)
+                /* This cache was never opened */
+                return false;
+        if (detail->last_close < seconds_since_boot() - 30)
+                /*
+                 * We allow for the possibility that someone might
+                 * restart a userspace daemon without restarting the
+                 * server; but after 30 seconds, we give up.
+                 */
+                 return false;
+        return true;
+}
+
 /*
  * register an upcall request to user-space and queue it up for read() by the
  * upcall daemon.
@@ -1109,10 +1126,9 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h,
         char *bp;
         int len;
 
-        if (atomic_read(&detail->readers) == 0 &&
-            detail->last_close < seconds_since_boot() - 30) {
-                        warn_no_listener(detail);
-                        return -EINVAL;
+        if (!cache_listeners_exist(detail)) {
+                warn_no_listener(detail);
+                return -EINVAL;
         }
 
         buf = kmalloc(PAGE_SIZE, GFP_KERNEL);