From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sat, 1 Sep 2007 01:19:04 +1000 From: David Chinner Subject: Re: [PATCH] Increase lockdep MAX_LOCK_DEPTH Message-ID: <20070831151904.GC734179@sgi.com> References: <46D79C62.1010304@sandeen.net> <1188542389.6112.44.camel@twins> <20070831135042.GD422459@sgi.com> <1188570831.6112.64.camel@twins> <20070831150511.GA734179@sgi.com> <1188572961.6112.72.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1188572961.6112.72.camel@twins> To: Peter Zijlstra Cc: David Chinner , Eric Sandeen , linux-kernel Mailing List , xfs-oss , Ingo Molnar List-ID: On Fri, Aug 31, 2007 at 05:09:21PM +0200, 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 :-) Ok.... > > Do semaphores (the flush locks) contribute to the lock depth > > counters? > > No, alas, we cannot handle semaphores in lockdep. Semaphores don't have > a strict owner, hence we cannot track them. This is one of the reasons > to rid ourselves of semaphores - that and there are very few cases where > the actual semantics of semaphores are needed. Most of the times code > using semaphores can be expressed with either a mutex or a completion. Yeah, and the flush lock is something we can't really use either of those for as we require both the multi-process lock/unlock behaviour and the mutual exclusion that a semaphore provides. So I guess that means it's only the ilock nesting that is of issue here, so that means right now a max lock depth of 40 would probably be ok.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group