linux-kernel - Re: [Patch v5 0/9] liblockdep: userspace lockdep

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Date:	Thu, 27 Jun 2013 09:55:45 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch v5 0/9] liblockdep: userspace lockdep

On 06/27/2013 05:07 AM, Ingo Molnar wrote:
>
> * Sasha Levin <sasha.levin@...cle.com> wrote:
>
>> On 06/26/2013 11:53 AM, Ingo Molnar wrote:
>>>> Ingo, I don't think I see anything holding this back; however I remember
>>>>> reading some email about people not liking stuff like this living in the
>>>>> tools/ directory or such.
>>>>>
>>>>> Will you pick this up?
>>> So I'd really be interested in how interesting/useful this is to userspace
>>> developers? Does it work for something complex as Firefox, or Apache, to
>>> the extent they make use of these locking APIs?
>>
>> So far I've tested it on Firefox, Apache, QEMU, LKVM, GCC and random
>> smallish programs. I haven't really done full testing for each of those,
>> but just made sure that liblockdep behaves as it supposed to. I'm
>> guessing that with further work it will dig up actual issues.
>
> The other issue is that with lock classes disabled you have to hit an
> actual deadlock to trigger any output.
>
> I.e. much of the power of lockdep is diminished :-/ When actual deadlocks
> are triggered then it's not particularly complex to debug user-space apps:
> gdb the hung task(s) and look at the backtraces.

Lock classes are disabled only if you're using the LD_PRELOAD method of
testing. If you actually re-compile your code with the library (by just
including the header and setting a #define to enable it) you will have
lock classes.


Thanks,
Sasha


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