linux-kernel - Re: [PATCH] debug work struct cancel deadlocks with lockdep

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Date:	Thu, 5 Jul 2007 10:53:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...sign.ru>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Sattler <tsattler@....de>
Subject: Re: [PATCH] debug work struct cancel deadlocks with lockdep


* Johannes Berg <johannes@...solutions.net> wrote:

> This adds a lockdep_map for each work struct in order to debug
> deadlocks like
>   my_function -> lock(); ...; cancel_work_sync(my_work)
> vs.
>   run_workqueue() -> my_work.f() -> ...; lock(); ...
> 
> which will deadlock if my_work.f() is invoked already but my_function()
> has acquired the lock already.
> 
> Signed-off-by: Johannes Berg <johannes@...solutions.net>

Acked-by: Ingo Molnar <mingo@...e.hu>

> +#ifdef CONFIG_LOCKDEP
> +/*
> + * HACK! This really should call lockdep_init_map() but can't
> + * because there's no requirement to initialise work structs
> + * at runtime. This works because subclass == 0.
> + *
> + * NB: because we have to copy the lockdep_map, setting .key
> + * here is required!
> + */

why do you consider this a hack? A static object is a static object, and 
its own address is its key. That's what we have for like 80% of all the 
spinlocks in the kernel. Static initialization is not as flexible as 
dynamic initialization, but the lockdep engine handles it. Am i missing 
something?

> +#define __WORK_INIT_LOCKDEP_MAP(n, k)				\
> +	.lockdep_map = {					\
> +		.name = n,					\
> +		.key = (void*) k,				\
> +	},

s/void*/void *

	Ingo
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