From: Li Jinlin lijinlin3@huawei.com
commit 02c6dcd543f8f051973ee18bfbc4dc3bd595c558 upstream.
We found a hang, the steps to reproduce 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 complete after step 4, but they hang.
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--
To fix this, we need to run queue before rescanning device when the device state changes to SDEV_RUNNING.
Link: https://lore.kernel.org/r/20210824025921.3277629-1-lijinlin3@huawei.com Fixes: f0f82e2476f6 ("scsi: core: Fix capacity set to zero after offlinining device") Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Li Jinlin lijinlin3@huawei.com Signed-off-by: Qiu Laibin qiulaibin@huawei.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/scsi/scsi_sysfs.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
--- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -788,12 +788,15 @@ store_state_field(struct device *dev, st 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);