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    Subject[PATCH 3.19.y-ckt 062/210] bcache: prevent crash on changing writeback_running
    Date
    3.19.8-ckt14 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Stefan Bader <stefan.bader@canonical.com>

    commit 8d16ce540c94c9d366eb36fc91b7154d92d6397b upstream.

    Added a safeguard in the shutdown case. At least while not being
    attached it is also possible to trigger a kernel bug by writing into
    writeback_running. This change adds the same check before trying to
    wake up the thread for that case.

    Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
    Cc: Kent Overstreet <kent.overstreet@gmail.com>
    Signed-off-by: Jens Axboe <axboe@fb.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/md/bcache/writeback.h | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h
    index 0a9dab1..073a042 100644
    --- a/drivers/md/bcache/writeback.h
    +++ b/drivers/md/bcache/writeback.h
    @@ -63,7 +63,8 @@ static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,

    static inline void bch_writeback_queue(struct cached_dev *dc)
    {
    - wake_up_process(dc->writeback_thread);
    + if (!IS_ERR_OR_NULL(dc->writeback_thread))
    + wake_up_process(dc->writeback_thread);
    }

    static inline void bch_writeback_add(struct cached_dev *dc)
    --
    1.9.1
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