linux-kernel - Re: [patch 11/33] fs: dcache scale subdirs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1277191631.1875.525.camel@laptop>
Date:	Tue, 22 Jun 2010 09:27:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	Nick Piggin <npiggin@...e.de>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, John Kacur <jkacur@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 11/33] fs: dcache scale subdirs

On Mon, 2010-06-21 at 23:02 -0700, john stultz wrote:
> On Mon, 2010-06-21 at 16:55 +0200, Peter Zijlstra wrote:
> > On Tue, 2010-06-22 at 00:48 +1000, Nick Piggin wrote:
> > > > Right, so I was staring at the -rt splat, so its John who created that
> > > > wreckage?
> > > 
> > > It was, but apparently they saw an RCU bug there somewhere and hit it
> > > with the big hammer. I haven't been able to reproduce it on a non-rt
> > > kernel yet, and I see yet why RCU is not good enough here.
> > 
> > John, could you describe the failure you spotted?
> 
> The problem was that the rcu_read_lock() on the dentry ascending wasn't
> preventing d_put/d_kill from removing entries from the parent node. So
> the next entry we tried to follow was invalid. So we were getting odd
> oopses from select_parent().
> 
> I'm not as familiar with the rcu rules there, so the patch I made just
> held the locks as it went down the chain. Not ideal of course, but still
> an improvement over the dcache_lock that was there prior.
> 
> Peter: I'm sorry, I've been out for a few days. Can you give me some
> background on what brought this up and what -rt splat you mean?

Well, you make lockdep very unhappy by locking multiple dentries
(unbounded number) all in the same lock class.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/