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 v2 send with Message-ID:
20210809141308.3700854-1-lijinlin3@xxxxxxxxxx
- Expanded code comment in store_state_field() as suggested by Bart
drivers/scsi/scsi_sysfs.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index ae9bfc658203..c0d31119d6d7 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -808,12 +808,15 @@ 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. Running the queue first is necessary
+ * because another thread may be waiting inside
+ * blk_mq_freeze_queue_wait() and because that call may be
+ * waiting for pending I/O to finish.
*/
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);
--
2.27.0
