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    Subject[patch 113/123] dm: free dm_io before bio_endio not after
    2.6.33-stable review patch.  If anyone has any objections, please let me know.

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

    From: Mikulas Patocka <mpatocka@redhat.com>

    commit a97f925a32aad2a37971d7bfb657006acf04e42d upstream.

    Free the dm_io structure before calling bio_endio() instead of after it,
    to ensure that the io_pool containing it is not referenced after it is
    freed.

    This partially fixes a problem described here
    https://www.redhat.com/archives/dm-devel/2010-February/msg00109.html

    thread 1:
    bio_endio(bio, io_error);
    /* scheduling happens */
    thread 2:
    close the device
    remove the device
    thread 1:
    free_io(md, io);

    Thread 2, when removing the device, sees non-empty md->io_pool (because the
    io hasn't been freed by thread 1 yet) and may crash with BUG in mempool_free.
    Thread 1 may also crash, when freeing into a nonexisting mempool.

    To fix this we must make sure that bio_endio() is the last call and
    the md structure is not accessed afterwards.

    There is another bio_endio in process_barrier, but it is called from the thread
    and the thread is destroyed prior to freeing the mempools, so this call is
    not affected by the bug.

    A similar bug exists with module unloads - the module may be unloaded
    immediately after bio_endio - but that is more difficult to fix.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Signed-off-by: Alasdair G Kergon <agk@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/md/dm.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/drivers/md/dm.c
    +++ b/drivers/md/dm.c
    @@ -635,8 +635,10 @@ static void dec_pending(struct dm_io *io
    if (!md->barrier_error && io_error != -EOPNOTSUPP)
    md->barrier_error = io_error;
    end_io_acct(io);
    + free_io(md, io);
    } else {
    end_io_acct(io);
    + free_io(md, io);

    if (io_error != DM_ENDIO_REQUEUE) {
    trace_block_bio_complete(md->queue, bio);
    @@ -644,8 +646,6 @@ static void dec_pending(struct dm_io *io
    bio_endio(bio, io_error);
    }
    }
    -
    - free_io(md, io);
    }
    }




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