linux-kernel - Re: [PATCH v2 (repost)] locking/lockdep: add debug_show_all_lock

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Message-ID: <8cfce359-2b55-5158-3a7f-d83a7be212f4@redhat.com>
Date:   Mon, 16 Jan 2023 22:28:01 -0500
From:   Waiman Long <longman@...hat.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 (repost)] locking/lockdep: add
 debug_show_all_lock_holders()

On 1/14/23 04:53, Tetsuo Handa wrote:
> On 2023/01/14 18:36, Ingo Molnar wrote:
>> Yeah, so note how you introduce a function with a parameter:
>>
>> 	void __debug_show_all_locks(bool show_stack)
>>
>> ... only to then *hide* the new parameter via helper functions:
>>
>> 	static inline void debug_show_all_locks(void)
>> 	{
>> 		__debug_show_all_locks(false);
>> 	}
>>
>> 	static inline void debug_show_all_lock_holders(void)
>> 	{
>> 		__debug_show_all_locks(true);
>> 	}
>>
>> ... which is a *strong* hint by our universe that the new parameter was
>> probably a bad idea to begin with.
>>
>> Given how small debug_show_all_locks() is to begin with, I'd suggest simply
>> duplicating the loop into debug_show_all_lock_holders() or so.
> Initial version at https://lkml.kernel.org/r/82af40cc-bf85-2b53-b8f9-dfc12e66a781@I-love.SAKURA.ne.jp
> was duplicating the loop.
>
> Waiman Long suggested me not to duplicate the loop at
> https://lkml.kernel.org/r/3e027453-fda4-3891-3ec3-5623f1525e56@redhat.com .
>
> Please talk with Waiman. I'm fine with either approach.

My original concern was that two functions are very similar with some 
minor difference. My suggestion was to use a common helper to reduce the 
code redundancy and future maintenance.

I do have some nits about the patch. The show_stack parameter isn't 
informative. Maybe you can use show_tasks as the parameter name since 
the major difference is the calling of sched_show_task().

Define a new helper like debug_show_all_locks_tasks(bool show_tasks), 
use it directly in check_hung_uninterruptible_tasks() and make 
debug_show_all_lock() call debug_show_all_locks_tasks().

Ingo, will that OK with you?

Cheers,
Longman