linux-kernel - Re: [RFC][PATCH 0/7] lockdep: Support recurise-read locks

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Date:	Fri, 22 Apr 2011 16:59:42 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	a.p.zijlstra@...llo.nl, rostedt@...dmis.org, tglx@...utronix.de,
	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 0/7] lockdep: Support recurise-read locks

2011/4/22 Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>:
>> But if you call locktest1/locktest2 firstly, the chain will not be established
>> just because recursive read is not added to prev->after.
>
> This part is not OK. At least, I think lockdep should be able to establish the
> chain when locktest1 is called AGAIN after locktest2 is called (i.e.
> "cat /proc/locktest1 /proc/locktest2 /proc/locktest1" case).

I guess lockdep will warn on "cat /proc/locktest1 /proc/locktest2
/proc/locktest1"

> But lockdep can
> establish the chain for only "cat /proc/locktest2 /proc/locktest1" case.
> I think there is a bug that prevents the lockdep from establishing the chain
> when locktest1 is called AGAIN after locktest2 is called.

If we want to fully support recursive read validation, it's a bug; but that
also mean some head-burning work :)

> If we can't fix the
> bug, we should consider periodically (or upon printing stall warning messages)
> revalidating already established chains.

I don't think periodically revalidating make sense; because lockdep do
validate everything real-time.

Thanks,
Yong



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