ceph: fix race during filling readdir cache

Readdir cache uses page cache to save dentry pointers. When adding
dentry pointers to middle of a page, we need to make sure the page
already exists. Otherwise the beginning part of the page will be
invalid pointers.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index cec68a6e20df..495decfc4b34 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -1349,15 +1349,20 @@ static int fill_readdir_cache(struct inode *dir, struct dentry *dn,
 
         if (!ctl->page || pgoff != page_index(ctl->page)) {
                 ceph_readdir_cache_release(ctl);
-                ctl->page  = grab_cache_page(&dir->i_data, pgoff);
+                if (idx == 0)
+                        ctl->page = grab_cache_page(&dir->i_data, pgoff);
+                else
+                        ctl->page = find_lock_page(&dir->i_data, pgoff);
                 if (!ctl->page) {
                         ctl->index = -1;
-                        return -ENOMEM;
+                        return idx == 0 ? -ENOMEM : 0;
                 }
                 /* reading/filling the cache are serialized by
                  * i_mutex, no need to use page lock */
                 unlock_page(ctl->page);
                 ctl->dentries = kmap(ctl->page);
+                if (idx == 0)
+                        memset(ctl->dentries, 0, PAGE_CACHE_SIZE);
         }
 
         if (req->r_dir_release_cnt == atomic64_read(&ci->i_release_count) &&