linux-kernel - Re: [PATCH V3 6/7] ublk_drv: add START_USER_RECOVERY and END_USER

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Date:   Tue, 20 Sep 2022 10:41:57 +0800
From:   Ziyang Zhang <ZiyangZhang@...ux.alibaba.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     axboe@...nel.dk, xiaoguang.wang@...ux.alibaba.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com
Subject: Re: [PATCH V3 6/7] ublk_drv: add START_USER_RECOVERY and
 END_USER_RECOVERY support

On 2022/9/19 21:03, Ming Lei wrote:
> 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@...ux.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.


OK, START_USER_RECOVERY just does cleanup stuff for a new process and
ublk_ch_release() does the similar thing since it is always called when chardev
is released. And our new process must open the chardev after it is released.

So (queue reinit, clearing ub->mm) can be done in ublk_ch_release().

Regards,
Zhang.