linux-kernel - Re: [PATCH] timer: silenct a lockdep splat with debugobjects

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Message-Id: <D3115315-12A9-43A9-9209-09553CF2C71C@lca.pw>
Date:   Fri, 13 Mar 2020 17:00:41 -0400
From:   Qian Cai <cai@....pw>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>, sboyd@...nel.org,
        rostedt@...dmis.org, hannes@...xchg.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] timer: silenct a lockdep splat with debugobjects



> On Mar 13, 2020, at 4:13 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Fri, Mar 13, 2020 at 03:32:52PM -0400, Qian Cai wrote:
>> Well, in mm/vmstat.c (init_mm_internals) case for example, it was initialized
>> as a static,
>> 
>> static DECLARE_DEFERRABLE_WORK(shepherd, vmstat_shepherd);
>> 
>> which will not call __debug_object_init(). 
> 
> Then fix that.
> 
> That is, all of:
> 
>  DECLARE_DEFERRABLE_WORK
>  KTHREAD_DELAYED_WORK_INIT
>  DEFINE_TIMER
> 
> are broken and need to go.

This looks invasive with so many callsites...

> 
> Unless of course, you can frob debugobjects such that we can provide the
> required storage through is_static_object() and modify the above static
> declarators to provide the storage.

I’ll explore this which looks more promising.

> 
> Or, fix that random crud to do the wakeup outside of the lock.

That is likely to be difficult until we can find a creative way to not “uglifying" the
random code by dropping locks in the middle etc just because of debugojects.

> 
> Plenty options..