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Date: Mon, 20 Jul 2015 18:23:53 +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: <20150720162353.GA1897@redhat.com>
References: <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> <20150717173117.GB30443@redhat.com> <20150717224015.GR7943@dastard>
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On 07/18, Dave Chinner wrote:
>
> On Fri, Jul 17, 2015 at 07:31:17PM +0200, Oleg Nesterov wrote:
> >
> > 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.
>
> Oh, I think I know what it was - when we duplicate a transaction for
> a rolling commit, we do it before committing the current transaction
> is committed. I *think* that used to take a second freeze reference,
> which only existed until the first transaction was committed. We do
> things a bit differently now - we hold a state flag on the
> transaction to indicate it needs to release the freeze reference
> when it is freed and we pass it to the new transaction so that the
> first transaction commit doesn't release it.

Just fyi, please do not assume I can understand the explanation above ;)

> So, yes, it may well be a stale comment now.

Perhaps. But this needs a separate change. Plus even if we remove this
hack, this code has other problems with lockdep.

I'll send the "lockdep" fixes/cleanup today, please review.

Oleg.