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

[Patrick Steinhardt]

On Sun, Jul 29, 2018 at 11:41:31AM +0200, Tomas Janousek wrote:
> 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.)

Huh, I did send out some more details on how I reproduce the
issue, but it seems like my mail didn't get through. While I
don't use laptop-mode-tools, I do have some custom hotplugging
scripts which do in fact enable runtime-PM for most devices.

Regards
Patrick

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