LOCKD: Fix a deadlock in nlm_traverse_files()

nlm_traverse_files() is not allowed to hold the nlm_file_mutex while calling
nlm_inspect file, since it may end up calling nlm_release_file() when
releaseing the blocks.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
(cherry picked from e558d3cde986e04f68afe8c790ad68ef4b94587a commit)

1 files changed, 9 insertions, 6 deletions

diff --git a/fs/lockd/svcsubs.c b/fs/lockd/svcsubs.c
index 2a4df9b3779a..01b4db9e5466 100644
--- a/fs/lockd/svcsubs.c
+++ b/fs/lockd/svcsubs.c
@@ -237,19 +237,22 @@ static int
 nlm_traverse_files(struct nlm_host *host, int action)
 {
         struct nlm_file *file, **fp;
-        int             i;
+        int i, ret = 0;
 
         mutex_lock(&nlm_file_mutex);
         for (i = 0; i < FILE_NRHASH; i++) {
                 fp = nlm_files + i;
                 while ((file = *fp) != NULL) {
+                        file->f_count++;
+                        mutex_unlock(&nlm_file_mutex);
+
                         /* Traverse locks, blocks and shares of this file
                          * and update file->f_locks count */
-                        if (nlm_inspect_file(host, file, action)) {
-                                mutex_unlock(&nlm_file_mutex);
-                                return 1;
-                        }
+                        if (nlm_inspect_file(host, file, action))
+                                ret = 1;
 
+                        mutex_lock(&nlm_file_mutex);
+                        file->f_count--;
                         /* No more references to this file. Let go of it. */
                         if (!file->f_blocks && !file->f_locks
                          && !file->f_shares && !file->f_count) {
@@ -262,7 +265,7 @@ nlm_traverse_files(struct nlm_host *host, int action)
                 }
         }
         mutex_unlock(&nlm_file_mutex);
-        return 0;
+        return ret;
 }
 
 /*