ext4: Fix deadlock in ext4_write_begin() and ext4_da_write_begin()

Functions ext4_write_begin() and ext4_da_write_begin() call
grab_cache_page_write_begin() without AOP_FLAG_NOFS. Thus it
can happen that page reclaim is triggered in that function
and it recurses back into the filesystem (or some other filesystem).
But this can lead to various problems as a transaction is already
started at that point. Add the necessary flag.

http://bugzilla.kernel.org/show_bug.cgi?id=11688

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index cbd2ca99d11351d757f36194173ee716d89bdc4f..51cdd13e1c31832243a38324b1d7ea3d7fd3c080 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1368,6 +1368,10 @@ retry:
                goto out;
        }
 
+       /* We cannot recurse into the filesystem as the transaction is already
+        * started */
+       flags |= AOP_FLAG_NOFS;
+
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page) {
                ext4_journal_stop(handle);
@@ -1377,7 +1381,7 @@ retry:
        *pagep = page;
 
        ret = block_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
-                                                       ext4_get_block);
+                               ext4_get_block);
 
        if (!ret && ext4_should_journal_data(inode)) {
                ret = walk_page_buffers(handle, page_buffers(page),
@@ -2667,6 +2671,9 @@ retry:
                ret = PTR_ERR(handle);
                goto out;
        }
+       /* We cannot recurse into the filesystem as the transaction is already
+        * started */
+       flags |= AOP_FLAG_NOFS;
 
        page = grab_cache_page_write_begin(mapping, index, flags);
        if (!page) {