linux-kernel - Re: [PATCH 03/32] locking/lockdep: lockdep_set_no_check

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Message-ID: <a7fcd53a-7680-49c5-dd93-489d75126c8d@redhat.com>
Date:   Tue, 9 May 2023 17:37:55 -0400
From:   Waiman Long <longman@...hat.com>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-bcachefs@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH 03/32] locking/lockdep: lockdep_set_no_check_recursion()

On 5/9/23 16:35, Kent Overstreet wrote:
> On Tue, May 09, 2023 at 04:27:46PM -0400, Waiman Long wrote:
>> On 5/9/23 16:18, Kent Overstreet wrote:
>>> On Tue, May 09, 2023 at 09:31:47PM +0200, Peter Zijlstra wrote:
>>>> On Tue, May 09, 2023 at 12:56:28PM -0400, Kent Overstreet wrote:
>>>>> This adds a method to tell lockdep not to check lock ordering within a
>>>>> lock class - but to still check lock ordering w.r.t. other lock types.
>>>>>
>>>>> This is for bcachefs, where for btree node locks we have our own
>>>>> deadlock avoidance strategy w.r.t. other btree node locks (cycle
>>>>> detection), but we still want lockdep to check lock ordering w.r.t.
>>>>> other lock types.
>>>>>
>>>> ISTR you had a much nicer version of this where you gave a custom order
>>>> function -- what happend to that?
>>> Actually, I spoke too soon; this patch and the other series with the
>>> comparison function solve different problems.
>>>
>>> For bcachefs btree node locks, we don't have a defined lock ordering at
>>> all - we do full runtime cycle detection, so we don't want lockdep
>>> checking for self deadlock because we're handling that but we _do_ want
>>> lockdep checking lock ordering of btree node locks w.r.t. other locks in
>>> the system.
>> Maybe you can use lock_set_novalidate_class() instead.
> No, we want that to go away, this is the replacement.

OK, you can mention that in the commit log then.

Cheers,
Longman