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

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Date:   Fri, 16 Sep 2022 10:46:18 -0700
From:   Boqun Feng <boqun.feng@...il.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ben Dooks <ben.dooks@...ive.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Xiaoming Ni <nixiaoming@...wei.com>,
        John Ogness <john.ogness@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH (repost)] locking/lockdep: add
 debug_show_all_lock_holders()

On Fri, Sep 16, 2022 at 10:51:14AM -0400, Waiman Long wrote:
[...]
> > 
> > I'm expecting lockdep to continue working without calling printk() even after
> > one of problem patterns (e.g. circular locking dependency) was printk()ed, so that
> > debug_show_all_locks()/debug_show_all_lock_holders() can call printk() when needed.
> > 
> > Changing debug_locks behavior is a future patch. For now, this patch alone
> > will help debugging Greg's usb.git#usb-testing tree which is generating
> > many "INFO: task hung in" reports.

The default behavior today does make sense: if the system has one
deadlock it should be fixed first before searching out another. So I
expect that changing debug_locks behavior would be configurable and we
keep the default as today.

> 
> Boqun is actually working on a modularization patch to make some lockdep
> checking still active even after a lockdep bug is reported. I think he will
> take into consideration about this request.
> 

Yes, this is one of the "problems" I try to resolve while cleaning up
the lockdep.

Regards,
Boqun

> Cheers,
> Longman
>