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Subject[ 40/54] ext4: avoid deadlock on sync-mounted FS w/o journal
3.0-stable review patch.  If anyone has any objections, please let me know.


From: Eric Sandeen <>

commit c1bb05a657fb3d8c6179a4ef7980261fae4521d7 upstream.

Processes hang forever on a sync-mounted ext2 file system that
is mounted with the ext4 module (default in Fedora 16).

I can reproduce this reliably by mounting an ext2 partition with
"-o sync" and opening a new file an that partition with vim. vim
will hang in "D" state forever. The same happens on ext4 without
a journal.

I am attaching a small patch here that solves this issue for me.
In the sync mounted case without a journal,
ext4_handle_dirty_metadata() may call sync_dirty_buffer(), which
can't be called with buffer lock held.

Also move mb_cache_entry_release inside lock to avoid race
fixed previously by 8a2bfdcb ext[34]: EA block reference count racing fix
Note too that ext2 fixed this same problem in 2006 with
b2f49033 [PATCH] fix deadlock in ext2

[ move mb_cache_entry_release before unlock, edit commit msg]
Signed-off-by: Eric Sandeen <>
Signed-off-by: "Theodore Ts'o" <>
Signed-off-by: Greg Kroah-Hartman <>

fs/ext4/xattr.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -487,18 +487,19 @@ ext4_xattr_release_block(handle_t *handl
ext4_free_blocks(handle, inode, bh, 0, 1,
+ unlock_buffer(bh);
} else {
le32_add_cpu(&BHDR(bh)->h_refcount, -1);
+ if (ce)
+ mb_cache_entry_release(ce);
+ unlock_buffer(bh);
error = ext4_handle_dirty_metadata(handle, inode, bh);
if (IS_SYNC(inode))
dquot_free_block(inode, 1);
ea_bdebug(bh, "refcount now=%d; releasing",
- if (ce)
- mb_cache_entry_release(ce);
- unlock_buffer(bh);
ext4_std_error(inode->i_sb, error);

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