linux-kernel - Re: [RFC 06/19] ktf: A simple debugfs interface to test results

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Message-ID: <20190815105225.GA16395@kroah.com>
Date:   Thu, 15 Aug 2019 12:52:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Knut Omang <knut.omang@...cle.com>
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Shreyans Devendra Doshi <0xinfosect0r@...il.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Kevin Hilman <khilman@...libre.com>,
        Hidenori Yamaji <hidenori.yamaji@...y.com>,
        Frank Rowand <frowand.list@...il.com>,
        Timothy Bird <Tim.Bird@...y.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Theodore Ts'o <tytso@....edu>, Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <sboyd@...nel.org>
Subject: Re: [RFC 06/19] ktf: A simple debugfs interface to test results

On Thu, Aug 15, 2019 at 12:35:26PM +0200, Knut Omang wrote:
> On Thu, 2019-08-15 at 10:49 +0200, Greg Kroah-Hartman wrote:
> > > I perfectly agree with you that reducing the hole for a race condition 
> > > is generally a bad idea, but from the above mail thread 
> > > it seems that's the only available choice for older kernels?
> > 
> > I have no idea, but please, do not use that pattern of code as it is
> > racy in all kernels, from all of time.
> 
> Ok, will remove it :-)
> 
> I tried in vain to find the commit from Al Viro that made the code safe,
> to identify which kernels that are safe from this issue,
> but he has a **lot** of commits, do you have a clue for what/where to look?
> 
> It will be good to have a mention/comment on this for future reference, 
> like the earliest kernel version where this is safe.

Always use a "newer" kernel to be "safe" and you will be fine :)

> Maybe we can even get rid of some more of the remaining of these too..
> (I notice there's 65 cases of 'if (!try_module_get(THIS_MODULE))'
> right now)

Something to put on a TODO list somewhere...

thanks,

greg k-h