linux-kernel - RE: [PATCH 3/5] fs, xfs: convert xlog_ticket.t_ref from atomic_t to refcount

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Date:   Thu, 9 Mar 2017 06:57:07 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Kees Cook <keescook@...omium.org>,
        Christoph Hellwig <hch@...radead.org>
CC:     "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        "David Windsor" <dwindsor@...il.com>
Subject: RE: [PATCH 3/5] fs, xfs: convert xlog_ticket.t_ref from atomic_t to
 refcount_t


> On Wed, Mar 8, 2017 at 7:50 AM, Christoph Hellwig <hch@...radead.org> wrote:
> >> -     ASSERT(atomic_read(&ticket->t_ref) > 0);
> >> -     atomic_inc(&ticket->t_ref);
> >> +     ASSERT(refcount_read(&ticket->t_ref) > 0);
> >> +     refcount_inc(&ticket->t_ref);
> >
> > With strict refcount semantics refcount_inc should check that
> > the count is larger than 0, otherwise we'd need to use
> > recount_inc_not_zero or whatever you're going to call it.
> >
> > Is that something the recount code does / could do?
> 
> Yes, refcount_inc() will not increment from 0 and WARNs. It looks like
> xfs's ASSERT is also a warn (though with XFS-specific formatting), so
> perhaps the ASSERT could be dropped? IIUC, Elena's approach to these
> changes was to be conservative about removing the existing checks.

I am removing the existing WARNs now where they are 100% not needed, but leaving the ones like this ASSERT, 
because I am thinking that you might have test cases that are dependent on these ASSERTs with specific formatting and I don't want to break them. 
If you don't need them, I can remove them also. 

Best Regards,
Elena

> 
> -Kees
> 
> --
> Kees Cook
> Pixel Security