On 05/08/2021 15:32, lijinlin3@xxxxxxxxxx wrote:
From: Li Jinlin<lijinlin3@xxxxxxxxxx>
We found a hang issue, the test steps are as follows:
1. echo "blocked" >/sys/block/sda/device/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
Step3 and Step4 should finish this work after Step4, but them hangs.
CPU#0 CPU#1 CPU#2
--------------- ---------------- ----------------
Step1: blocking device
Step2: dd xxxx
^^^^^^ get request
q_usage_counter++
Step3: 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
Step4: 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--
Step3 and Step4 wait for each other, caused hangs.
This requires run queue frist to fix this issue when the device state
frist ?
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>
Signed-off-by: Wu Bo<wubo40@xxxxxxxxxx>
what kind of SoB is this?
---
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.
A bit more description of the IO hang would be useful
*/
if (ret == 0 && state == SDEV_RUNNING) {
- scsi_rescan_device(dev);
blk_mq_run_hw_queues(sdev->request_queue, true);
+ scsi_rescan_device(dev);
This would not have happened if scsi_rescan_device() was ran outside the
mutex lock region, like I suggested originally.
Indeed, I doubt blk_mq_run_hw_queues() needs to be run with the sdev
state_mutex held either.
}
mutex_unlock(&sdev->state_mutex);
--
