linux-kernel - Re: [PATCH] Increase lockdep MAX_LOCK

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Message-ID: <46D82F9A.9090606@sandeen.net>
Date:	Fri, 31 Aug 2007 10:11:22 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	David Chinner <dgc@....com>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	xfs-oss <xfs@....sgi.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Increase lockdep MAX_LOCK_DEPTH

Peter Zijlstra wrote:
> On Sat, 2007-09-01 at 01:05 +1000, David Chinner wrote:
> 
>>> Trouble is, we'd like to have a sane upper bound on the amount of held
>>> locks at any one time, obviously this is just wanting, because a lot of
>>> lock chains also depend on the number of online cpus...
>> Sure - this is an obvious case where it is valid to take >30 locks at
>> once in a single thread. In fact, worst case here we are taking twice this
>> number of locks - we actually take 2 per inode (ilock and flock) so a
>> full 32 inode cluster free would take >60 locks in the middle of this
>> function and we should be busting this depth couter limit all the
>> time. 
> 
> I think this started because jeffpc couldn't boot without XFS busting
> lockdep :-)
> 
>> Do semaphores (the flush locks) contribute to the lock depth
>> counters? 
> 
> No, alas, we cannot handle semaphores in lockdep.

That explains why 40 was enough for me, I guess :)

-Eric
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