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    Subject[PATCH 002 of 6] md: Fix use-after-free bug when dropping an rdev from an md array.

    Due to possible deadlock issues we need to use a schedule work to
    kobject_del an 'rdev' object from a different thread.

    A recent change means that kobject_add no longer gets a refernce, and
    kobject_del doesn't put a reference. Consequently, we need to
    explicitly hold a reference to ensure that the last reference isn't
    dropped before the scheduled work get a chance to call kobject_del.

    Also, rename delayed_delete to md_delayed_delete to that it is more
    obvious in a stack trace which code is to blame.

    Cc: Al Viro <viro@ZenIV.linux.org.uk>
    Signed-off-by: Neil Brown <neilb@suse.de>

    ### Diffstat output
    ./drivers/md/md.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff .prev/drivers/md/md.c ./drivers/md/md.c
    --- .prev/drivers/md/md.c 2008-01-14 12:23:53.000000000 +1100
    +++ ./drivers/md/md.c 2008-01-14 12:24:17.000000000 +1100
    @@ -1421,10 +1421,11 @@ static int bind_rdev_to_array(mdk_rdev_t
    return err;
    }

    -static void delayed_delete(struct work_struct *ws)
    +static void md_delayed_delete(struct work_struct *ws)
    {
    mdk_rdev_t *rdev = container_of(ws, mdk_rdev_t, del_work);
    kobject_del(&rdev->kobj);
    + kobject_put(&rdev->kobj);
    }

    static void unbind_rdev_from_array(mdk_rdev_t * rdev)
    @@ -1443,7 +1444,8 @@ static void unbind_rdev_from_array(mdk_r
    /* We need to delay this, otherwise we can deadlock when
    * writing to 'remove' to "dev/state"
    */
    - INIT_WORK(&rdev->del_work, delayed_delete);
    + INIT_WORK(&rdev->del_work, md_delayed_delete);
    + kobject_get(&rdev->kobj);
    schedule_work(&rdev->del_work);
    }

    @@ -3688,7 +3690,7 @@ static int do_md_stop(mddev_t * mddev, i
    sysfs_remove_link(&mddev->kobj, nm);
    }

    - /* make sure all delayed_delete calls have finished */
    + /* make sure all md_delayed_delete calls have finished */
    flush_scheduled_work();

    export_array(mddev);

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