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

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Date:   Wed, 25 Jul 2018 18:13:02 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "ps@....im" <ps@....im>, "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>
Subject: Re: [PATCH] block: fix NPE when resuming SCSI devices using blk-mq

On Fri, 2018-07-13 at 15:29 +0200, Patrick Steinhardt wrote:
> When power management for SCSI is enabled and if a device uses blk-mq,
> it is possible to trigger a `NULL` pointer exception when resuming that
> device. The NPE is triggered when trying to dereference the `request_fn`
> function pointer of the device's `request_queue`:
> 
>     __blk_run_queue_uncond:470
>     __blk_run_queue:490
>     blk_post_runtime_resume:3889
>     sdev_runtime_resume:263
>     scsi_runtime_resume:275
> 
> When the SCSI device is being allocated by `scsi_alloc_sdev`, the
> device's request queue will either be initialized via
> `scsi_mq_alloc_queue` or `scsi_old_alloc_queue`. But the `request_fn`
> member of the request queue is in fact only being set in
> `scsi_old_alloc_queue`, which will then later cause the mentioned NPE.
> 
> Fix the issue by checking whether the `request_fn` is set in
> `__blk_run_queue_uncond`. In case it is unset, we'll silently return and
> not try to invoke the callback, thus fixing the NPE.

Which kernel version are you using? Can you check whether the following two
commits are in your kernel tree?

* 4fd41a8552af ("SCSI: Fix NULL pointer dereference in runtime PM"; December
  2015).
* 765e40b675a9 ("block: disable runtime-pm for blk-mq"; July 2017).

Thanks,

Bart.