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Date:   Fri, 3 May 2019 18:15:15 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Evan Green <evgreen@...omium.org>,
        linux-block <linux-block@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Jens Axboe <axboe@...nel.dk>
Subject: Re: blkdev_get deadlock

On 5/3/19 10:47 AM, Evan Green wrote:
> Hey blockies,
  ^^^^^^^^^^^^

That's the weirdest greeting I have encountered so far on the
linux-block mailing list.

> I'm seeing a hung task in the kernel, and I wanted to share it in case
> it's a known issue. I'm still trying to wrap my head around the stacks
> myself. This is our Chrome OS 4.19 kernel, which is admittedly not
> 100% vanilla mainline master, but we try to keep it pretty close.
> 
> I can reproduce this reliably within our chrome OS installer, where
> it's trying to dd from my system disk (NVMe) to a loop device backed
> by a removable UFS card (4kb sectors) in a USB dongle.

Although this is not the only possible cause such hangs are often caused
by a block driver or SCSI LLD not completing a request. A list of
pending requests can be obtained e.g. by running the attached script.

Bart.

View attachment "list-pending-block-requests" of type "text/plain" (1501 bytes)

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