Commit c1bb05a6 authored Feb 20, 2012 by Eric Sandeen Committed by Theodore Ts'o Feb 20, 2012

ext4: avoid deadlock on sync-mounted FS w/o journal



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

Signed-off-by:  <Martin.Wilck@ts.fujitsu.com>
[sandeen@redhat.com: move mb_cache_entry_release before unlock, edit commit msg]
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

parent a0ade1de

fs/ext4/xattr.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -484,18 +484,19 @@ ext4_xattr_release_block(handle_t handle, struct inode inode,
		ext4_free_blocks(handle, inode, bh, 0, 1,
		EXT4_FREE_BLOCKS_METADATA \|
		EXT4_FREE_BLOCKS_FORGET);
		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))
		ext4_handle_sync(handle);
		dquot_free_block(inode, 1);
		ea_bdebug(bh, "refcount now=%d; releasing",
		le32_to_cpu(BHDR(bh)->h_refcount));
		if (ce)
		mb_cache_entry_release(ce);
		}
		unlock_buffer(bh);
		out:
		ext4_std_error(inode->i_sb, error);
		return;