linux-kernel - Re: [PATCH] block: fix NPE when resuming SCSI devices using blk-mq

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Message-ID: <20180729094131.4kwuukzgfgtisgya@notes.lisk.in>
Date:   Sun, 29 Jul 2018 11:41:31 +0200
From:   Tomas Janousek <tomi@...i.cz>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Patrick Steinhardt <ps@....im>, Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: fix NPE when resuming SCSI devices using blk-mq

Hi,

On Fri, Jul 13, 2018 at 09:41:41PM +0800, Ming Lei wrote:
> Now runtime PM is disabled for blk-mq/scsi_mq, not sure how this issue is
> triggered on your machine.

While Patrick did miss the following patch:

* 765e40b675a9 ("block: disable runtime-pm for blk-mq"; July 2017).

there is at least one other way to trigger it -- enable laptop-mode-tools
or tlp which enable runtime-pm for all devices.

The "disable runtime-pm for blk-mq" only disables it _by_default_, but doesn't
prevent it from being enabled again from user-space, which it is unless one
manually blacklists sd devices from runtime-pm enablement. It's bitten a few
people already: https://github.com/rickysarraf/laptop-mode-tools/issues/123

(I found this thread because I'm also getting the NULL pointer dereference at
00000000000001a8 on resume from suspend.)

-- 
Tomáš Janoušek, a.k.a. Pivník, a.k.a. Liskni_si, http://work.lisk.in/