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)chardev 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 <[email protected]>
---
drivers/block/ublk_drv.c | 116 ++++++++++++++++++++++++++++++++++
include/uapi/linux/ublk_cmd.h | 3 +-
2 files changed, 118 insertions(+), 1 deletion(-)
diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
index 3d7b067e0b99..f31d80f66fd6 100644
--- a/drivers/block/ublk_drv.c
+++ b/drivers/block/ublk_drv.c
@@ -1862,6 +1862,116 @@ 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);
+ /* 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;
+ init_completion(&ub->completion);
+ ret = 0;
+ out_unlock:
+ mutex_unlock(&ub->mutex);
+ ublk_put_device(ub);
+ return ret;
+}
+
+static int ublk_ctrl_end_recovery(struct io_uring_cmd *cmd)
+{
+ struct ublksrv_ctrl_cmd *header = (struct ublksrv_ctrl_cmd *)cmd->cmd;
+ int ublksrv_pid = (int)header->data[0];
+ struct ublk_device *ub;
+ int ret = -EINVAL;
+
+ ub = ublk_get_device_from_id(header->dev_id);
+ if (!ub)
+ return ret;
+
+ pr_devel("%s: Waiting for new ubq_daemons(nr: %d) are ready, dev id %d...\n",
+ __func__, ub->dev_info.nr_hw_queues, header->dev_id);
+ /* wait until new ubq_daemon sending all FETCH_REQ */
+ wait_for_completion_interruptible(&ub->completion);
+ pr_devel("%s: All new ubq_daemons(nr: %d) are ready, dev id %d\n",
+ __func__, ub->dev_info.nr_hw_queues, header->dev_id);
+
+ mutex_lock(&ub->mutex);
+ if (!ublk_can_use_recovery(ub))
+ goto out_unlock;
+
+ if (ub->dev_info.state != UBLK_S_DEV_QUIESCED) {
+ ret = -EBUSY;
+ goto out_unlock;
+ }
+ ub->dev_info.ublksrv_pid = ublksrv_pid;
+ pr_devel("%s: new ublksrv_pid %d, dev id %d\n",
+ __func__, ublksrv_pid, header->dev_id);
+ blk_mq_unquiesce_queue(ub->ub_disk->queue);
+ pr_devel("%s: queue unquiesced, dev id %d.\n",
+ __func__, header->dev_id);
+ blk_mq_kick_requeue_list(ub->ub_disk->queue);
+ ub->dev_info.state = UBLK_S_DEV_LIVE;
+ schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);
+ ret = 0;
+ out_unlock:
+ mutex_unlock(&ub->mutex);
+ ublk_put_device(ub);
+ return ret;
+}
+
static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
unsigned int issue_flags)
{
@@ -1903,6 +2013,12 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd,
case UBLK_CMD_SET_PARAMS:
ret = ublk_ctrl_set_params(cmd);
break;
+ case UBLK_CMD_START_USER_RECOVERY:
+ ret = ublk_ctrl_start_recovery(cmd);
+ break;
+ case UBLK_CMD_END_USER_RECOVERY:
+ ret = ublk_ctrl_end_recovery(cmd);
+ break;
default:
break;
}
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h
index 332370628757..8f88e3a29998 100644
--- a/include/uapi/linux/ublk_cmd.h
+++ b/include/uapi/linux/ublk_cmd.h
@@ -17,7 +17,8 @@
#define UBLK_CMD_STOP_DEV 0x07
#define UBLK_CMD_SET_PARAMS 0x08
#define UBLK_CMD_GET_PARAMS 0x09
-
+#define UBLK_CMD_START_USER_RECOVERY 0x10
+#define UBLK_CMD_END_USER_RECOVERY 0x11
/*
* IO commands, issued by ublk server, and handled by ublk driver.
*
--
2.27.0
On 2022/9/23 14:15, 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)chardev 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 <[email protected]>
Let me explain why we still need two ctrl-cmds: START_USER_RECOVERY
and END_USER_RECOVERY:
(1) They are easy to use and understand. Just like calling
a)ADD_DEV, b)start daemon c)START_DEV, we can recover a device by
a)START_USER_RECOVERY b)start new daemon c)END_USER_RECOVERY.
IMO, START_USER_RECOVERY can guide user whether to start a new daemon.
Without it, user must directly start a new daemon. He may fail here
because /dev/ublkc* is not released. So a retry is necessary here.
But I think that let the user retry by sending START_USER_RECOVERY
instead of opening /dev/ublkc* is more reasonable.
(2) Handling put_task_struct(ubq_daemon) is hard in ublk_ch_release().
Assume all ioucmds have been issued back to userspace and a crash happens,
ublk_ch_release() can be called immediately here and ubq_daemon is
freed. But monoitor_work may be running now. Dealing with UAF on
ubq_daemon in monitor_work may be difficult. But handling
put_task_struct(ubq_daemon) in START_USER_RECOVERY solves the problem
because monitor_work is sure to be canceled. Besides, here is no race
with ublk_deinit_queue() since it cannot be called if ub's state is
QUIESCED.
Regards,
Zhang
On Fri, Sep 23, 2022 at 02:15:04PM +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)chardev 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 <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Thanks,
Ming