On 2021/8/9 22:13, Li Jinlin wrote:
> From: Li Jinlin <lijinlin3@xxxxxxxxxx>
>
> We found a hang issue, the test steps are as follows:
> 1. blocking device via scsi_device_set_state()
> 2. dd if=/dev/sda of=/mnt/t.log bs=1M count=10
> 3. echo none > /sys/block/sda/queue/scheduler
> 4. echo "running" >/sys/block/sda/device/state
>
> Step 3 and 4 should finish this work after step 4, but they hangs.
>
> CPU#0 CPU#1 CPU#2
> --------------- ---------------- ----------------
> Step 1: blocking device
>
> Step 2: dd xxxx
> ^^^^^^ get request
> q_usage_counter++
>
> Step 3: switching scheculer
> elv_iosched_store
> elevator_switch
> blk_mq_freeze_queue
> blk_freeze_queue
> > blk_freeze_queue_start
> ^^^^^^ mq_freeze_depth++
>
> > blk_mq_run_hw_queues
> ^^^^^^ can't run queue when dev blocked
>
> > blk_mq_freeze_queue_wait
> ^^^^^^ Hang here!!!
> wait q_usage_counter==0
>
> Step 4: running device
> store_state_field
> scsi_rescan_device
> scsi_attach_vpd
> scsi_vpd_inquiry
> __scsi_execute
> blk_get_request
> blk_mq_alloc_request
> blk_queue_enter
> ^^^^^^ Hang here!!!
> wait mq_freeze_depth==0
>
> blk_mq_run_hw_queues
> ^^^^^^ dispatch IO, q_usage_counter will reduce to zero
>
> blk_mq_unfreeze_queue
> ^^^^^ mq_freeze_depth--
>
> Step 3 and 4 wait for each other.
>
> To fix this, we need to run queue before rescanning device when the device
> state changes to SDEV_RUNNING.
>
> Fixes: f0f82e2476f6 ("scsi: core: Fix capacity set to zero after offlinining device")
> Signed-off-by: Li Jinlin <lijinlin3@xxxxxxxxxx>
> Signed-off-by: Qiu Laibin <qiulaibin@xxxxxxxxxx>
> ---
> changes since v1 send with Message-ID:
> 20210805143231.1713299-1-lijinlin3@xxxxxxxxxx
>
> - Modify the subject to make it distinct
> - Modify the message to fix typo and make it distinct
> - Reduce the number of SOB
>
> drivers/scsi/scsi_sysfs.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index c3a710bceba0..aa701582c950 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -809,12 +809,12 @@ store_state_field(struct device *dev, struct device_attribute *attr,
> ret = scsi_device_set_state(sdev, state);
> /*
> * If the device state changes to SDEV_RUNNING, we need to
> - * rescan the device to revalidate it, and run the queue to
> - * avoid I/O hang.
> + * run the queue to avoid I/O hang, and rescan the device
> + * to revalidate it.
> */
> if (ret == 0 && state == SDEV_RUNNING) {
> - scsi_rescan_device(dev);
> blk_mq_run_hw_queues(sdev->request_queue, true);
> + scsi_rescan_device(dev);
> }
> mutex_unlock(&sdev->state_mutex);
>
>
Ping.
Thanks,
Li Jinlin
