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



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