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commit02c6dcd543upstream. 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:f0f82e2476("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>
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.