linux-kernel - Re: [PATCH v2] pstore/ram: no timekeeping calls when unavailable

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Message-ID: <20121117025355.GC29966@lizard>
Date:	Fri, 16 Nov 2012 18:53:55 -0800
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] pstore/ram: no timekeeping calls when unavailable

On Fri, Nov 09, 2012 at 05:26:53PM -0800, Kees Cook wrote:
[....]
> >> @@ -171,7 +171,13 @@ static size_t ramoops_write_kmsg_hdr(struct
> >> persistent_ram_zone *prz)
> >>         struct timeval timestamp;
> >>         size_t len;
> >>
> >> -       do_gettimeofday(&timestamp);
> >> +       /* Handle dumping before timekeeping has resumed. */
> >> +       if (unlikely(timekeeping_suspended)) {
> >> +               timestamp.tv_sec = 0;
> >> +               timestamp.tv_usec = 0;
> >> +       } else
> >> +               do_gettimeofday(&timestamp);
> >> +
> >
> > Would nulling out the timestamp be better done in do_gettimeofday()?  That
> > way we don't have to export timekeeping internals and users would get
> > something more sane for this corner case.
> 
> Well... I'm not sure. If we don't want to expose the
> timekeeping_suspended variable, maybe we need a function to check
> this? I think it's probably better to find the users of timekeeping
> that could call it when suspended. That's why I figured the BUG was
> there. Very very few things should be attempting to call gettimeofday
> in a place where it might be suspended. As such, it seems like those
> things should be able to determine how to handle it. Maybe not
> everything would be sensible to get back 0s.
> 
> In this particular case, I'm fine with removing the BUG and returning
> 0 instead, since that's fine for ramoops. :)

In the lack of agreement on kernel/time/timekeeping.c change, I can't
apply the patch. And personally I tend to agree that doing this workaround
in the pstore code is odd. How about introducing ___do_gettimeofday() that
is safe to call when suspened, and the func would have good kernel doc
comments explaining the purpose of it?

Thanks,
Anton.
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