linux-kernel - Re: [patch V2 6/7] fs/jbd2: Make state lock a spinlock

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Message-ID: <20190802133714.GN25064@quack2.suse.cz>
Date:   Fri, 2 Aug 2019 15:37:14 +0200
From:   Jan Kara <jack@...e.cz>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jan Kara <jack@...e.cz>, 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>,
        Theodore Tso <tytso@....edu>, Mark Fasheh <mark@...heh.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Joel Becker <jlbec@...lplan.org>, linux-ext4@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [patch V2 6/7] fs/jbd2: Make state lock a spinlock

On Thu 01-08-19 20:12:11, Thomas Gleixner wrote:
> On Thu, 1 Aug 2019, Jan Kara wrote:
> > On Thu 01-08-19 03:01:32, Thomas Gleixner wrote:
> > > As almost all functions which use this lock have a journal head pointer
> > > readily available, it makes more sense to remove the lock helper inlines
> > > and write out spin_*lock() at all call sites.
> > > 
> > 
> > Just a heads up that I didn't miss this patch. Just it has some bugs and I
> > figured that rather than explaining to you subtleties of jh lifetime it is
> > easier to fix up the problems myself since you're probably not keen on
> > becoming jbd2 developer ;)... which was more complex than I thought so I'm
> > not completely done yet. Hopefuly tomorrow.
> 
> I'm curious where I was too naive :)

Well, the most obvious where places where the result ended up being like

	jbd2_journal_put_journal_head(jh);
	spin_unlock(&jh->state_lock);

That's possible use-after-free.

But there were also other more subtle places where
jbd2_journal_put_journal_head() was not directly visible as it was hidden
inside journal list handling functions such as __jbd2_journal_refile_buffer()
or so. And these needed some more work.

Anyway, I'm now done fixing up the patch, doing some xfstests runs to verify
things didn't break in any obvious way...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR