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02c6dcd543
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:
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History
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.