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SubjectRe: [PATCH BUGFIX 3/6] block, bfq: get extra ref to prevent a queue from being freed during a group move
Hello.

On 31.01.2020 10:24, Paolo Valente wrote:
> In bfq_bfqq_move(), the bfq_queue, say Q, to be moved to a new group
> may happen to be deactivated in the scheduling data structures of the
> source group (and then activated in the destination group). If Q is
> referred only by the data structures in the source group when the
> deactivation happens, then Q is freed upon the deactivation.
>
> This commit addresses this issue by getting an extra reference before
> the possible deactivation, and releasing this extra reference after Q
> has been moved.
>
> Tested-by: Chris Evich <cevich@redhat.com>
> Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
> ---
> block/bfq-cgroup.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index e1419edde2ec..8ab7f18ff8cb 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -651,6 +651,12 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct
> bfq_queue *bfqq,
> bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
> false, BFQQE_PREEMPTED);
>
> + /*
> + * get extra reference to prevent bfqq from being freed in
> + * next possible deactivate
> + */
> + bfqq->ref++;

Shouldn't this be hidden under some macro (bfq_get_queue_ref(), for
instance) and also converted from int into refcount_t?

> +
> if (bfq_bfqq_busy(bfqq))
> bfq_deactivate_bfqq(bfqd, bfqq, false, false);
> else if (entity->on_st)
> @@ -670,6 +676,8 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct
> bfq_queue *bfqq,
>
> if (!bfqd->in_service_queue && !bfqd->rq_in_driver)
> bfq_schedule_dispatch(bfqd);
> + /* release extra ref taken above */
> + bfq_put_queue(bfqq);
> }
>
> /**

--
Oleksandr Natalenko (post-factum)

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