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Subject: Re: [PATCH] timer: silenct a lockdep splat with debugobjects
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <20200313201314.GE5086@worktop.programming.kicks-ass.net>
Date:   Fri, 13 Mar 2020 17:00:41 -0400
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>, sboyd@kernel.org,
        rostedt@goodmis.org, hannes@cmpxchg.org,
        linux-kernel@vger.kernel.org
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Message-Id: <D3115315-12A9-43A9-9209-09553CF2C71C@lca.pw>
References: <20200313154221.1566-1-cai@lca.pw>
 <20200313180811.GD12521@hirez.programming.kicks-ass.net>
 <4FFD109D-EAC1-486F-8548-AA1F5E024120@lca.pw>
 <20200313201314.GE5086@worktop.programming.kicks-ass.net>
To:     Peter Zijlstra <peterz@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Mar 13, 2020, at 4:13 PM, Peter Zijlstra <peterz@infradead.org> =
wrote:
>=20
> 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,
>>=20
>> static DECLARE_DEFERRABLE_WORK(shepherd, vmstat_shepherd);
>>=20
>> which will not call __debug_object_init().=20
>=20
> Then fix that.
>=20
> That is, all of:
>=20
>  DECLARE_DEFERRABLE_WORK
>  KTHREAD_DELAYED_WORK_INIT
>  DEFINE_TIMER
>=20
> are broken and need to go.

This looks invasive with so many callsites...

>=20
> 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=E2=80=99ll explore this which looks more promising.

>=20
> 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 =
=E2=80=9Cuglifying" the
random code by dropping locks in the middle etc just because of =
debugojects.

>=20
> Plenty options..