linux-kernel - Re: [PATCH 2/2] block: hold queue lock while iterating in diskstats

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Date:   Thu, 20 Jan 2022 21:51:18 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Daniel Wagner <dwagner@...e.de>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH 2/2] block: hold queue lock while iterating in
 diskstats_show

On Thu, Jan 20, 2022 at 02:19:36PM +0100, Daniel Wagner wrote:
> Hi Ming,
> 
> On Thu, Jan 20, 2022 at 08:56:03PM +0800, Ming Lei wrote:
> [323467.255527] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [323467.255538] #PF: supervisor read access in kernel mode
> [323467.255541] #PF: error_code(0x0000) - not-present page
> [323467.255544] PGD 0 P4D 0 
> [323467.255550] Oops: 0000 [#1] SMP PTI
> [323467.255555] CPU: 13 PID: 17640 Comm: iostat Kdump: loaded Tainted: G          IOE  X    5.3.18-59.27-default #1 SLE15-SP3
> [323467.255559] Hardware name: Dell Inc. PowerEdge R940xa/08XR9M, BIOS 2.12.2 07/12/2021
> [323467.255569] RIP: 0010:blk_mq_queue_tag_busy_iter+0x1e4/0x2e0

Then Can you figure out where blk_mq_queue_tag_busy_iter+0x1e4 points to
in source code? And what is NULL pointer?

With this kind of info, we may know the root cause.

Thanks,
Ming