linux-kernel - Re: Coccinelle: semantic patch for missing of_node

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Date:   Mon, 20 May 2019 21:53:40 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Sasha Levin <sashal@...nel.org>
cc:     Pavel Machek <pavel@....cz>, wen.yang99@....com.cn,
        Markus.Elfring@....de, cocci@...teme.lip6.fr,
        linux-kernel@...r.kernel.org,
        Gilles Muller <Gilles.Muller@...6.fr>,
        yamada.masahiro@...ionext.com, michal.lkml@...kovi.net,
        nicolas.palix@...g.fr
Subject: Re: Coccinelle: semantic patch for missing of_node_put



On Mon, 20 May 2019, Sasha Levin wrote:

> On Mon, May 20, 2019 at 11:52:37AM +0200, Julia Lawall wrote:
> >
> >
> > On Mon, 20 May 2019, Pavel Machek wrote:
> >
> > > Hi!
> > >
> > > > A semantic patch has no access to comments.  The only thing I can see to
> > > > do is to use python to interact with some external tools.  For example,
> > > > you could write some code to collect the comments in a file and the
> > > lines
> > > > on which they occur, and then get the comment that most closely precedes
> > > > the start of the function.
> > >
> > > How dangerous is missing of_node_put? AFAICT it will only result into
> > > very small, one-time memory leak, right?
> > >
> > > Could we make sure these patches are _not_ going to stable? Leaking
> > > few bytes once per boot is not really a serious bug.
> >
> > Sasha,
> >
> > Probably patches that add only of_node_put should not be auto selected for
> > stable.
>
> I can filter them out, but those are fixes, right? Why are we concerned
> about them making it into -stable?

One of them may have introduced a crash.  If there is a bad reference
count manipulation elsewhere, then fixing one could cause a later
incorrect one to make a double free.

On the other hand, I don't know if the one that seemed to cause a crash
really caused a crash.  It was detected by syzkaller, and it is also
possible that git bisect ended up at the wrong place.

In any case, forgetting an of_node_put will normally just waste a little
memory, so probably stable kernels don't care.

julia