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    SubjectRe: [PATCH V3 6/7] ublk_drv: add START_USER_RECOVERY and END_USER_RECOVERY support
    On Tue, Sep 13, 2022 at 12:17:06PM +0800, ZiyangZhang wrote:
    > START_USER_RECOVERY and END_USER_RECOVERY are two new control commands
    > to support user recovery feature.
    >
    > After a crash, user should send START_USER_RECOVERY, it will:
    > (1) check if (a)current ublk_device is UBLK_S_DEV_QUIESCED which was
    > set by quiesce_work and (b)the file struct is released.
    > (2) reinit all ubqs, including:
    > (a) put the task_struct and reset ->ubq_daemon to NULL.
    > (b) reset all ublk_io.
    > (3) reset ub->mm to NULL.
    >
    > Then, user should start a new process and send FETCH_REQ on each
    > ubq_daemon.
    >
    > Finally, user should send END_USER_RECOVERY, it will:
    > (1) wait for all new ubq_daemons getting ready.
    > (2) update ublksrv_pid
    > (3) unquiesce the request queue and expect incoming ublk_queue_rq()
    > (4) convert ub's state to UBLK_S_DEV_LIVE
    >
    > Note: we can handle STOP_DEV between START_USER_RECOVERY and
    > END_USER_RECOVERY. This is helpful to users who cannot start new process
    > after sending START_USER_RECOVERY ctrl-cmd.
    >
    > Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
    > ---
    > drivers/block/ublk_drv.c | 116 +++++++++++++++++++++++++++++++++++++++
    > 1 file changed, 116 insertions(+)
    >
    > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
    > index 4409a130d0b6..3a3af80ee938 100644
    > --- a/drivers/block/ublk_drv.c
    > +++ b/drivers/block/ublk_drv.c
    > @@ -1961,6 +1961,116 @@ static int ublk_ctrl_set_params(struct io_uring_cmd *cmd)
    > return ret;
    > }
    >
    > +static void ublk_queue_reinit(struct ublk_device *ub, struct ublk_queue *ubq)
    > +{
    > + int i;
    > +
    > + WARN_ON_ONCE(!(ubq->ubq_daemon && ubq_daemon_is_dying(ubq)));
    > + /* All old ioucmds have to be completed */
    > + WARN_ON_ONCE(ubq->nr_io_ready);
    > + pr_devel("%s: prepare for recovering qid %d\n", __func__, ubq->q_id);
    > + /* old daemon is PF_EXITING, put it now */
    > + put_task_struct(ubq->ubq_daemon);
    > + /* We have to reset it to NULL, otherwise ub won't accept new FETCH_REQ */
    > + ubq->ubq_daemon = NULL;
    > +
    > + for (i = 0; i < ubq->q_depth; i++) {
    > + struct ublk_io *io = &ubq->ios[i];
    > +
    > + /* forget everything now and be ready for new FETCH_REQ */
    > + io->flags = 0;
    > + io->cmd = NULL;
    > + io->addr = 0;
    > + }
    > +}
    > +
    > +static int ublk_ctrl_start_recovery(struct io_uring_cmd *cmd)
    > +{
    > + struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
    > + struct ublk_device *ub;
    > + int ret = -EINVAL;
    > + int i;
    > +
    > + ub = ublk_get_device_from_id(header->dev_id);
    > + if (!ub)
    > + return ret;
    > +
    > + mutex_lock(&ub->mutex);
    > + if (!ublk_can_use_recovery(ub))
    > + goto out_unlock;
    > + /*
    > + * START_RECOVERY is only allowd after:
    > + *
    > + * (1) UB_STATE_OPEN is not set, which means the dying process is exited
    > + * and related io_uring ctx is freed so file struct of /dev/ublkcX is
    > + * released.
    > + *
    > + * (2) UBLK_S_DEV_QUIESCED is set, which means the quiesce_work:
    > + * (a)has quiesced request queue
    > + * (b)has requeued every inflight rqs whose io_flags is ACTIVE
    > + * (c)has requeued/aborted every inflight rqs whose io_flags is NOT ACTIVE
    > + * (d)has completed/camceled all ioucmds owned by ther dying process
    > + */
    > + if (test_bit(UB_STATE_OPEN, &ub->state) ||
    > + ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
    > + ret = -EBUSY;
    > + goto out_unlock;
    > + }
    > + pr_devel("%s: start recovery for dev id %d.\n", __func__, header->dev_id);
    > + for (i = 0; i < ub->dev_info.nr_hw_queues; i++)
    > + ublk_queue_reinit(ub, ublk_get_queue(ub, i));
    > + /* set to NULL, otherwise new ubq_daemon cannot mmap the io_cmd_buf */
    > + ub->mm = NULL;
    > + ub->nr_queues_ready = 0;

    I am wondering why you don't move the above(queue reinit, clearing ub->mm)
    into ublk_ch_release(), and looks it is more clean to clear this stuff
    there. Meantime I guess one control command might be enough for user
    recovery.


    Thanks,
    Ming

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