linux-kernel - Re: "blk-mq: fix tag_get wait task can't be awakened" causes hangs

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Date:   Tue, 25 Jan 2022 10:15:41 -0500
From:   "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        axboe@...nel.dk, linux-block@...r.kernel.org,
        QiuLaibin <qiulaibin@...wei.com>
Cc:     akpm@...ux-foundation.org, bvanassche@....org, hare@...e.de,
        john.garry@...wei.com, linux-kernel@...r.kernel.org,
        martin.petersen@...cle.com, ming.lei@...hat.com,
        Daniel Palmer <daniel@...f.com>
Subject: Re: "blk-mq: fix tag_get wait task can't be awakened" causes hangs

Excerpts from QiuLaibin's message of January 24, 2022 11:08 pm:
> Hi Alex
> 
> 1、Please help to import this structure:
> 
> blk_mq_tags <= 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
> 
> cat /sys/block/sda/mq/0/nr_tags
>                 __ <= Change it to the problem device

The affected device returns 1. My understanding is that mq does not work 
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
├─sda1        8:1    0 [snip]  0 part
├─sda2        8:2    0 [snip]  0 part
└─sda3        8:3    0 [snip]  0 part
sdb           8:16   0 [snip]  0 disk
├─sdb1        8:17   0 [snip]  0 part
├─sdb2        8:18   0 [snip]  0 part
├─sdb3        8:19   0 [snip]  0 part
└─sdb4        8:20   0 [snip]  0 part
sdc           8:32   1 [snip]  0 disk
├─sdc1        8:33   1 [snip]  0 part
└─sdc2        8:34   1 [snip]  0 part
nvme0n1     259:0    0 [snip]  0 disk
├─nvme0n1p1 259:1    0 [snip]  0 part
└─nvme0n1p2 259:2    0 [snip]  0 part
  └─root    254:0    0 [snip]  0 crypt /

> 2、Please 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、Please help to try the attachment patch and see if it can be reproduced.

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

> Thanks.

Cheers,
Alex.