Re: [RFC PATCH 1/9] ublk_drv: check 'current' instead of 'ubq_daemon'

Ming Lei
2022-08-29T02:14:16Z

On Wed, Aug 24, 2022 at 01:47:36PM +0800, ZiyangZhang wrote:
> This check is not atomic. So with recovery feature, ubq_daemon may be
> updated simultaneously by recovery task. Instead, check 'current' is
> safe here because 'current' never changes.
>
> Also add comment explaining this check, which is really important for
> understanding recovery feature.
>
> Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
> ---
> drivers/block/ublk_drv.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 6a4a94b4cdf4..c39b67d7133d 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -645,14 +645,22 @@ static inline void __ublk_rq_task_work(struct request *req)
> struct ublk_device *ub = ubq->dev;
> int tag = req->tag;
> struct ublk_io *io = &ubq->ios[tag];
> - bool task_exiting = current != ubq->ubq_daemon || ubq_daemon_is_dying(ubq);
> unsigned int mapped_bytes;
>
> pr_devel("%s: complete: op %d, qid %d tag %d io_flags %x addr %llx\n",
> __func__, io->cmd->cmd_op, ubq->q_id, req->tag, io->flags,
> ublk_get_iod(ubq, req->tag)->addr);
>
> - if (unlikely(task_exiting)) {
> + /*
> + * Task is exiting if either:
> + *
> + * (1) current != ubq_daemon.
> + * io_uring_cmd_complete_in_task() tries to run task_work
> + * in a workqueue if ubq_daemon(cmd's task) is PF_EXITING.
> + *
> + * (2) current->flags & PF_EXITING.
> + */
> + if (unlikely(current != ubq->ubq_daemon || current->flags & PF_EXITING)) {

Reviewed-by: Ming Lei <ming.lei@redhat.com>

Thanks,
Ming