linux-ext4 - Re: [patch V2 6/7] fs/jbd2: Make state lock a spinlock

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Date:   Fri, 2 Aug 2019 17:29:43 +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>,
        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 Fri, 2 Aug 2019, Jan Kara wrote:

> 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.

Duh yes.

> 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...

Very appreciated.

Thanks,

	tglx