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>

1 files changed, 11 insertions, 2 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 17802a96af9f..5c0d17066f4a 100644
--- 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