linux-kernel - Re: [6.16.9 / 6.17.0 PANIC REGRESSION] block: fix lockdep warning caused by lock dependency in elv_iosched

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Message-ID: <05b105b8-1382-4ef3-aaaa-51b7b1927036@linux.ibm.com>
Date: Thu, 2 Oct 2025 21:00:34 +0530
From: Nilay Shroff <nilay@...ux.ibm.com>
To: Kyle Sanderson <kyle.leet@...il.com>, linux-block@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>, axboe@...nel.dk
Cc: hch@....de, ming.lei@...hat.com, hare@...e.de, sth@...ux.ibm.com,
        gjoyce@....com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [6.16.9 / 6.17.0 PANIC REGRESSION] block: fix lockdep warning
 caused by lock dependency in elv_iosched_store



On 10/1/25 6:35 PM, Kyle Sanderson wrote:
> On 9/30/2025 10:20 PM, Kyle Sanderson wrote:
>> On 7/30/2025 12:46 AM, Nilay Shroff wrote:
>>> To address this, move all sched_tags allocations and deallocations outside
>>> of both the ->elevator_lock and the ->freeze_lock.
>>
>> Hi Nilay,
>>
>> I am coming off of a 36 hour travel stint, and 6.16.7 (I do not have that log, and it mightily messed up my xfs root requiring offline repair), 6.16.9, and 6.17.0 simply do not boot on my system. After unlocking with LUKS I get this panic consistently and immediately, and I believe this is the problematic commit which was unfortunately carried to the previous and current stable. I am using this udev rule: `ACTION=="add|change", KERNEL=="sd*[!0-9]|sr*|nvme*", ATTR{queue/ scheduler}="bfq"`
> 
> Hi Greg,
> 
> Slept for a couple hours. This appears to be well known in block (the fix is in the 6.18 pull) that it is causing panics on stable, and didn't make it back to 6.17 past the initial merge window (as well as 6.16).
> 
> Presumably adjusting the request depth isn't common (if this is indeed the problem)?
> 
> I also have ACTION=="add|change", KERNEL=="sd*[!0-9]|sr*|nvme*", ATTR{queue/nr_requests}="1024" as a udev rule.
> 
So the above udev rule suggests that you're updating
nr_requests which do update the queue depth. 

> Jens, is this the only patch from August that is needed to fix this panic?
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-6.18/block&id=ba28afbd9eff2a6370f23ef4e6a036ab0cfda409
> 
Greg, I think we should have the above commit ba28afbd9eff ("blk-mq: fix 
blk_mq_tags double free while nr_requests grown") backported to the 6.16.x
stable kernel, if it hasn't yet queued up. 

Thanks,
--Nilay