linux-ext4 - Re: [patch V2 7/7] fs/jbd2: Free journal head outside of locked region

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Date:   Thu, 1 Aug 2019 20:08:30 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jan Kara <jack@...e.cz>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Julia Cartwright <julia@...com>, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org, Theodore Tso <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Mark Fasheh <mark@...heh.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Joel Becker <jlbec@...lplan.org>
Subject: Re: [patch V2 7/7] fs/jbd2: Free journal head outside of locked
 region

On Thu, 1 Aug 2019, Jan Kara wrote:
> On Thu 01-08-19 03:01:33, Thomas Gleixner wrote:
> > On PREEMPT_RT bit-spinlocks have the same semantics as on PREEMPT_RT=n,
> > i.e. they disable preemption. That means functions which are not safe to be
> > called in preempt disabled context on RT trigger a might_sleep() assert.
> Looks mostly good. Just a small suggestion for simplification below:
> 
> > @@ -2559,11 +2568,14 @@ void jbd2_journal_put_journal_head(struc
> >  	J_ASSERT_JH(jh, jh->b_jcount > 0);
> >  	--jh->b_jcount;
> >  	if (!jh->b_jcount) {
> > -		__journal_remove_journal_head(bh);
> > +		size_t b_size = __journal_remove_journal_head(bh);
> > +
> >  		jbd_unlock_bh_journal_head(bh);
> > +		journal_release_journal_head(jh, b_size);
> >  		__brelse(bh);
> 
> The bh is pinned until you call __brelse(bh) above and bh->b_size doesn't
> change during the lifetime of the buffer. So there's no need of
> fetching bh->b_size in __journal_remove_journal_head() and passing it back.
> You can just:
> 
> 		journal_release_journal_head(jh, bh->b_size);

Ah. Nice. I assumed that this would be possible, but then my ignorance
induced paranoia won.

Thanks,

	tglx