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Date: Fri, 17 Jul 2015 19:31:17 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>, Dave Hansen <dave.hansen@linux.intel.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Daniel Wagner <daniel.wagner@bmw-carit.de>,
        Davidlohr Bueso <dave@stgolabs.net>, Ingo Molnar <mingo@redhat.com>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 0/4] change sb_writers to use percpu_rw_semaphore
Message-ID: <20150717173117.GB30443@redhat.com>
References: <20150714104810.GB24369@quack.suse.cz> <20150714133731.GA24837@redhat.com> <55A57C50.1080406@linux.intel.com> <20150714212249.GA18441@redhat.com> <55A581F9.3090507@linux.intel.com> <20150715064705.GA22609@quack.suse.cz> <20150715181920.GA1797@redhat.com> <20150716072654.GE22847@quack.suse.cz> <20150716173256.GA17753@redhat.com> <20150717012742.GV3902@dastard>
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On 07/17, Dave Chinner wrote:
>
> On Thu, Jul 16, 2015 at 07:32:56PM +0200, Oleg Nesterov wrote:
> >
> > 	#ifdef CONFIG_LOCKDEP
> > 		/*
> > 		 * We want lockdep to tell us about possible deadlocks with freezing but
> > 		 * it's it bit tricky to properly instrument it. Getting a freeze protection
> > 		 * works as getting a read lock but there are subtle problems. XFS for example
> > 		 * gets freeze protection on internal level twice in some cases, which is OK
>
> Sorry, I've missed something here - where is XFS nesting
> sb_start_intwrite() calls?

Heh ;) I too tried to understand thi but failed. I was not surprized,
I know nothing about fs/.

Dave, I didn't write this comment. Please look at acquire_freeze_lock().
If we can remove this logic - great! but this needs a separate change.

Oleg.