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SubjectRe: [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

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