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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 <sandeen@redhat.com>

    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

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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,
    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;



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