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SubjectRe: [PATCH] pstore: use ktime_get_real_fast_ns() instead of __getnstimeofday()
On Thu, 9 Nov 2017, Kees Cook wrote:
> On Thu, Nov 9, 2017 at 4:46 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Fri, 10 Nov 2017, Arnd Bergmann wrote:
> >> On Fri, Nov 10, 2017 at 12:00 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
> >> > Hmm, no. None of the regular accessor functions can be called from NMI
> >> > context safely.
> >>
> >> Right, that's what I mean: it must not get called from NMI context, but it
> >> currently is, at least for this case:
> >>
> >> NMI handler:
> >> something bad
> >> panic()
> >> kmsg_dump()
> >> pstore_dump()
> >> pstore_record_init()
> >> __getnstimeofday()
> >>
> >> I should probably add that to the changelog text ;-)
> >
> > Indeed.
>
> Er, so, is this safe to call there? I've had to fix this a few times
> now, so if using ktime_get_real_fast_ns() can be used here (and
> doesn't return 0) then this is easily an improvement over the existing
> "maybe read 0" case pstore has now.

ktime_get_real_fast_ns() is NMI safe and returns

before timekeeping_suspend(): correct time

after timekeeping_suspend(): timestamp which was frozen in
timekeeping_suspend()

after timekeeping_resume(): correct time

Thanks,

tglx

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