linux-kernel - Re: [RESEND PATCH 01/11] kernel:lockdep:print the shortest dependency chain if finding a circle

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Date:	Mon, 13 Jul 2009 21:51:12 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [RESEND PATCH 01/11] kernel:lockdep:print the shortest dependency 
	chain if finding a circle

2009/7/13 Ingo Molnar <mingo@...e.hu>:
>
> * Ming Lei <tom.leiming@...il.com> wrote:
>> No, as you said, the shortest circle is not very important, and it
>> is just a byproduct and we have no reason to reject it.
>
> It's a nice byproduct, beyond the primary advantage of not being a
> stack based recursion check.
>
> I think this patch-set is great, and there's just one more step
> needed to make it round: it would be nice to remove the limitation
> of maximum number of locks held per task. (MAX_LOCK_DEPTH)

IMHO,  it seems that removing the MAX_LOCK_DEPTH limitation is another
topic,  and is nothing to do with this patch-set.  We may still make it round
with the limitation like before.

Can we plan to remove the limitation of MAX_LOCK_DEPTH after merging
the patch-set?

Thanks.

>
> The way we could do it is to split out this bit of struct task:
>
> #ifdef CONFIG_LOCKDEP
> # define MAX_LOCK_DEPTH 48UL
>        u64 curr_chain_key;
>        int lockdep_depth;
>        unsigned int lockdep_recursion;
>        struct held_lock held_locks[MAX_LOCK_DEPTH];
>        gfp_t lockdep_reclaim_gfp;
> #endif
>
> into a separate 'struct lockdep_state' structure, and allocate it
> dynamically during fork with a initial pre-set size of say 64 locks
> depth. If we hit that limit, we'd double the allocation threshold,
> which would cause a larger structure to be allocated for all newly
> allocated tasks.
>
> ( This means that the task that hits this threshold needs to have
>  lockdep disabled until it exits - but that's OK. )
>
>        Ingo
>

-- 
Lei Ming
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