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    Subject[PATCH 4.9 050/177] writeback: fix memory leak in wb_queue_work()
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: Tahsin Erdogan <tahsin@google.com>


    [ Upstream commit 4a3a485b1ed0e109718cc8c9d094fa0f552de9b2 ]

    When WB_registered flag is not set, wb_queue_work() skips queuing the
    work, but does not perform the necessary clean up. In particular, if
    work->auto_free is true, it should free the memory.

    The leak condition can be reprouced by following these steps:

    mount /dev/sdb /mnt/sdb
    /* In qemu console: device_del sdb */
    umount /dev/sdb

    Above will result in a wb_queue_work() call on an unregistered wb and
    thus leak memory.

    Reported-by: John Sperbeck <jsperbeck@google.com>
    Signed-off-by: Tahsin Erdogan <tahsin@google.com>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Jens Axboe <axboe@fb.com>
    Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/fs-writeback.c | 35 +++++++++++++++++++++--------------
    1 file changed, 21 insertions(+), 14 deletions(-)

    --- a/fs/fs-writeback.c
    +++ b/fs/fs-writeback.c
    @@ -173,19 +173,33 @@ static void wb_wakeup(struct bdi_writeba
    spin_unlock_bh(&wb->work_lock);
    }

    +static void finish_writeback_work(struct bdi_writeback *wb,
    + struct wb_writeback_work *work)
    +{
    + struct wb_completion *done = work->done;
    +
    + if (work->auto_free)
    + kfree(work);
    + if (done && atomic_dec_and_test(&done->cnt))
    + wake_up_all(&wb->bdi->wb_waitq);
    +}
    +
    static void wb_queue_work(struct bdi_writeback *wb,
    struct wb_writeback_work *work)
    {
    trace_writeback_queue(wb, work);

    - spin_lock_bh(&wb->work_lock);
    - if (!test_bit(WB_registered, &wb->state))
    - goto out_unlock;
    if (work->done)
    atomic_inc(&work->done->cnt);
    - list_add_tail(&work->list, &wb->work_list);
    - mod_delayed_work(bdi_wq, &wb->dwork, 0);
    -out_unlock:
    +
    + spin_lock_bh(&wb->work_lock);
    +
    + if (test_bit(WB_registered, &wb->state)) {
    + list_add_tail(&work->list, &wb->work_list);
    + mod_delayed_work(bdi_wq, &wb->dwork, 0);
    + } else
    + finish_writeback_work(wb, work);
    +
    spin_unlock_bh(&wb->work_lock);
    }

    @@ -1875,16 +1889,9 @@ static long wb_do_writeback(struct bdi_w

    set_bit(WB_writeback_running, &wb->state);
    while ((work = get_next_work_item(wb)) != NULL) {
    - struct wb_completion *done = work->done;
    -
    trace_writeback_exec(wb, work);
    -
    wrote += wb_writeback(wb, work);
    -
    - if (work->auto_free)
    - kfree(work);
    - if (done && atomic_dec_and_test(&done->cnt))
    - wake_up_all(&wb->bdi->wb_waitq);
    + finish_writeback_work(wb, work);
    }

    /*

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