linux-kernel - Re: [PATCH RFC 0/4] change sb_writers to use percpu_rw

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Message-ID: <20150717173117.GB30443@redhat.com>
Date:	Fri, 17 Jul 2015 19:31:17 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Jan Kara <jack@...e.cz>, Dave Hansen <dave.hansen@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/4] change sb_writers to use percpu_rw_semaphore

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.

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