nfsd: Fix a soft lockup race in nfsd_file_mark_find_or_create()

If nfsd_file_mark_find_or_create() keeps winning the race for the
nfsd_file_fsnotify_group->mark_mutex against nfsd_file_mark_put()
then it can soft lock up, since fsnotify_add_inode_mark() ends
up always finding an existing entry.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 9c2b29e..f275c11 100644 (file)
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -132,9 +132,13 @@ nfsd_file_mark_find_or_create(struct nfsd_file *nf)
                                                 struct nfsd_file_mark,
                                                 nfm_mark));
                        mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
-                       fsnotify_put_mark(mark);
-                       if (likely(nfm))
+                       if (nfm) {
+                               fsnotify_put_mark(mark);
                                break;
+                       }
+                       /* Avoid soft lockup race with nfsd_file_mark_put() */
+                       fsnotify_destroy_mark(mark, nfsd_file_fsnotify_group);
+                       fsnotify_put_mark(mark);
                } else
                        mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);