linux-kernel - Re: [PATCH 2/3] Increase lockdep limits: MAX_LOCK

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Date:	Tue, 7 Jul 2009 16:36:03 +0100
From:	Joao Correia <joaomiguelcorreia@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Américo Wang <xiyou.wangcong@...il.com>
Subject: Re: [PATCH 2/3] Increase lockdep limits: MAX_LOCK_DEPTH

Im running into this in places as diverse as modprobe, swapper, udevd
and ip6tables-restore. It doesnt happen always on the same one, and
the stack traces dont point to an (apparent) common point, hence me
flagging this as a limit that is just being triggered due to increased
lockdep usage.

Joao Correia



On Tue, Jul 7, 2009 at 4:29 PM, Peter Zijlstra<a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2009-07-07 at 16:25 +0100, Joao Correia wrote:
>> (Applies to current Linus tree, as of 2.6.31-rc2)
>>
>> As a result of increasing MAX_STACK_TRACE_ENTRIES on the previous
>> patch, another limit surfaced as being hit too soon.
>> This patch increases MAX_LOCK_DEPTH, being hit by false positives, and
>> turning off the locking correctness validator.
>>
>> The new value is arbitrary, but I believe the old one was too. Given
>> the amount of changes happening with regards to the usage of lockdep,
>> the previous limit is just too low and keeping it that way would
>> defeat the purpose of lockdep.
>>
>>
>> Signed-off-by: Joao Correia <joaomiguelcorreia@...il.com>
>
> NAK, find the site that triggers this and fix it. holding more than 48
> locks at any one time is silly.
>
>> ---
>>  include/linux/sched.h |    2 +-
>>  1 files changes, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 0085d75..304231b 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1367,7 +1367,7 @@ struct task_struct {
>>         int softirq_context;
>>  #endif
>>  #ifdef CONFIG_LOCKDEP
>> -# define MAX_LOCK_DEPTH 48UL
>> +# define MAX_LOCK_DEPTH 96UL
>>         u64 curr_chain_key;
>>         int lockdep_depth;
>>         unsigned int lockdep_recursion;
>> ---
>
>
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