ext4: Take page lock before looking at attached buffer_heads flags

In order to check whether the buffer_heads are mapped we need to hold
page lock. Otherwise a reclaim can cleanup the attached buffer_heads.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 17802a9..5c0d170 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5286,12 +5286,21 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
        else
                len = PAGE_CACHE_SIZE;
 
+       lock_page(page);
+       /*
+        * return if we have all the buffers mapped. This avoid
+        * the need to call write_begin/write_end which does a
+        * journal_start/journal_stop which can block and take
+        * long time
+        */
        if (page_has_buffers(page)) {
-               /* return if we have all the buffers mapped */
                if (!walk_page_buffers(NULL, page_buffers(page), 0, len, NULL,
-                                      ext4_bh_unmapped))
+                                       ext4_bh_unmapped)) {
+                       unlock_page(page);
                        goto out_unlock;
+               }
        }
+       unlock_page(page);
        /*
         * OK, we need to fill the hole... Do write_begin write_end
         * to do block allocation/reservation.We are not holding