linux-kernel - Re: WARNING: CPU: 3 PID: 1 at block/blk-mq-cpumap.c:90 blk_mq_map_hw

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Message-ID: <9434298a-6756-4fdb-a412-ec34994e8376@flourine.local>
Date: Thu, 23 Jan 2025 08:59:41 +0100
From: Daniel Wagner <dwagner@...e.de>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Christoph Hellwig <hch@....de>, LKML <linux-kernel@...r.kernel.org>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Daniel Wagner <wagi@...nel.org>, Hannes Reinecke <hare@...e.de>, 
	Ming Lei <ming.lei@...hat.com>, John Garry <john.g.garry@...cle.com>, 
	Jens Axboe <axboe@...nel.dk>
Subject: Re: WARNING: CPU: 3 PID: 1 at block/blk-mq-cpumap.c:90
 blk_mq_map_hw_queues+0xf3/0x100

On Wed, Jan 22, 2025 at 05:58:17PM -0500, Steven Rostedt wrote:
> On Wed, 22 Jan 2025 12:54:45 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > Not sure its related. I can see how reproducible this is, and if it is, I
> > can try to bisect it.
> 
> I bisected it down to: a5665c3d150c98 ("virtio: blk/scsi: replace
> blk_mq_virtio_map_queues with blk_mq_map_hw_queues")
> 
> And reverting that as well as:
> 
>   9bc1e897a821f ("blk-mq: remove unused queue mapping helpers")
> 
> It booted fine.

In the previous tests you just comment out the WARN_ON_ONCE or did you
also replace blk_mq_clear_mq_map with blk_mq_map_queues? The
blk_mq_clear_mq_map will map all queues to CPU 0 and if you offline CPU
0, there is nothing left to serve the hctx. I'll try to reproduce your
test and see if I my idea works.

Thanks,
Daniel