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    Subject[PATCH 3.10 37/38] Btrfs: do not move em to modified list when unpinning
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Josef Bacik <jbacik@fb.com>

    commit a28046956c71985046474283fa3bcd256915fb72 upstream.

    We use the modified list to keep track of which extents have been modified so we
    know which ones are candidates for logging at fsync() time. Newly modified
    extents are added to the list at modification time, around the same time the
    ordered extent is created. We do this so that we don't have to wait for ordered
    extents to complete before we know what we need to log. The problem is when
    something like this happens

    log extent 0-4k on inode 1
    copy csum for 0-4k from ordered extent into log
    sync log
    commit transaction
    log some other extent on inode 1
    ordered extent for 0-4k completes and adds itself onto modified list again
    log changed extents
    see ordered extent for 0-4k has already been logged
    at this point we assume the csum has been copied
    sync log
    crash

    On replay we will see the extent 0-4k in the log, drop the original 0-4k extent
    which is the same one that we are replaying which also drops the csum, and then
    we won't find the csum in the log for that bytenr. This of course causes us to
    have errors about not having csums for certain ranges of our inode. So remove
    the modified list manipulation in unpin_extent_cache, any modified extents
    should have been added well before now, and we don't want them re-logged. This
    fixes my test that I could reliably reproduce this problem with. Thanks,

    Signed-off-by: Josef Bacik <jbacik@fb.com>
    Signed-off-by: Chris Mason <clm@fb.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/btrfs/extent_map.c | 2 --
    1 file changed, 2 deletions(-)

    --- a/fs/btrfs/extent_map.c
    +++ b/fs/btrfs/extent_map.c
    @@ -263,8 +263,6 @@ int unpin_extent_cache(struct extent_map
    if (!em)
    goto out;

    - if (!test_bit(EXTENT_FLAG_LOGGING, &em->flags))
    - list_move(&em->list, &tree->modified_extents);
    em->generation = gen;
    clear_bit(EXTENT_FLAG_PINNED, &em->flags);
    em->mod_start = em->start;



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