fscache: don't leak cookie access refs if invalidation is in progress or failed

It's possible for a request to invalidate a fscache_cookie will come in
while we're already processing an invalidation. If that happens we
currently take an extra access reference that will leak. Only call
__fscache_begin_cookie_access if the FSCACHE_COOKIE_DO_INVALIDATE bit
was previously clear.

Also, ensure that we attempt to clear the bit when the cookie is
"FAILED" and put the reference to avoid an access leak.

Fixes: 85e4ea10 ("fscache: Fix invalidation/lookup race")
Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>

fs/fscache/cookie.c

@@ -739,6 +739,9 @@ static void fscache_cookie_state_machine(struct fscache_cookie *cookie)
 		fallthrough;
 
 	case FSCACHE_COOKIE_STATE_FAILED:
+		if (test_and_clear_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
+			fscache_end_cookie_access(cookie, fscache_access_invalidate_cookie_end);
+
 		if (atomic_read(&cookie->n_accesses) != 0)
 			break;
 		if (test_bit(FSCACHE_COOKIE_DO_RELINQUISH, &cookie->flags)) {
@@ -1063,8 +1066,8 @@ void __fscache_invalidate(struct fscache_cookie *cookie,
 		return;
 
 	case FSCACHE_COOKIE_STATE_LOOKING_UP:
+		if (!test_and_set_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags))
 			__fscache_begin_cookie_access(cookie, fscache_access_invalidate_cookie);
-		set_bit(FSCACHE_COOKIE_DO_INVALIDATE, &cookie->flags);
 		fallthrough;
 	case FSCACHE_COOKIE_STATE_CREATING:
 		spin_unlock(&cookie->lock);