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Date:   Tue, 25 Jan 2022 10:15:41 -0500
From:   "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>
Subject: Re: "blk-mq: fix tag_get wait task can't be awakened" causes hangs
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        axboe@kernel.dk, linux-block@vger.kernel.org,
        QiuLaibin <qiulaibin@huawei.com>
Cc:     akpm@linux-foundation.org, bvanassche@acm.org, hare@suse.de,
        john.garry@huawei.com, linux-kernel@vger.kernel.org,
        martin.petersen@oracle.com, ming.lei@redhat.com,
        Daniel Palmer <daniel@0x0f.com>
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        <1643040870.3bwvk3sis4.none@localhost>
        <78cafe94-a787-e006-8851-69906f0c2128@huawei.com>
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Excerpts from QiuLaibin's message of January 24, 2022 11:08 pm:
> Hi Alex
>=20
> 1=E3=80=81Please help to import this structure:
>=20
> blk_mq_tags <=3D request_queue->blk_mq_hw_ctx->blk_mq_tags

I don't understand what you mean.

> If there is no kernel dump, help to see the value of
>=20
> cat /sys/block/sda/mq/0/nr_tags
>                 __ <=3D Change it to the problem device

The affected device returns 1. My understanding is that mq does not work=20
with legacy non-UAS devices.

> And how many block devices in total by lsblk.

My device topology roughly looks like:

NAME        MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINTS
sda           8:0    0 [snip]  0 disk
=E2=94=9C=E2=94=80sda1        8:1    0 [snip]  0 part
=E2=94=9C=E2=94=80sda2        8:2    0 [snip]  0 part
=E2=94=94=E2=94=80sda3        8:3    0 [snip]  0 part
sdb           8:16   0 [snip]  0 disk
=E2=94=9C=E2=94=80sdb1        8:17   0 [snip]  0 part
=E2=94=9C=E2=94=80sdb2        8:18   0 [snip]  0 part
=E2=94=9C=E2=94=80sdb3        8:19   0 [snip]  0 part
=E2=94=94=E2=94=80sdb4        8:20   0 [snip]  0 part
sdc           8:32   1 [snip]  0 disk
=E2=94=9C=E2=94=80sdc1        8:33   1 [snip]  0 part
=E2=94=94=E2=94=80sdc2        8:34   1 [snip]  0 part
nvme0n1     259:0    0 [snip]  0 disk
=E2=94=9C=E2=94=80nvme0n1p1 259:1    0 [snip]  0 part
=E2=94=94=E2=94=80nvme0n1p2 259:2    0 [snip]  0 part
  =E2=94=94=E2=94=80root    254:0    0 [snip]  0 crypt /

> 2=E3=80=81Please describe in detail how to reproduce the issue,

1. Plug in the device.
2. Execute Show Blocked Tasks. udev is stuck.

> And what type of USB device?

It is a cheap unbranded USB flash drive.

> 3=E3=80=81Please help to try the attachment patch and see if it can be re=
produced.

From a quick test, it appears to resolve the issue.

> Thanks.

Cheers,
Alex.