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SubjectRe: [121/127] [S390] nmi: fix clock comparator revalidation
On Wed, Dec 08, 2010 at 09:04:28AM +0100, Heiko Carstens wrote:
> On Tue, Dec 07, 2010 at 04:45:07PM -0800, Greg KH wrote:
> > 2.6.32-stable review patch. If anyone has any objections, please let us know.
> >
> > ------------------
> >
> > From: Heiko Carstens <heiko.carstens@de.ibm.com>
> >
> > commit e8129c642155616d9e2160a75f103e127c8c3708 upstream.
> >
> > On each machine check all registers are revalidated. The save area for
> > the clock comparator however only contains the upper most seven bytes
> > of the former contents, if valid.
> > Therefore the machine check handler uses a store clock instruction to
> > get the current time and writes that to the clock comparator register
> > which in turn will generate an immediate timer interrupt.
> > However within the lowcore the expected time of the next timer
> > interrupt is stored. If the interrupt happens before that time the
> > handler won't be called. In turn the clock comparator won't be
> > reprogrammed and therefore the interrupt condition stays pending which
> > causes an interrupt loop until the expected time is reached.
> >
> > On NOHZ machines this can result in unresponsive machines since the
> > time of the next expected interrupted can be a couple of days in the
> > future.
> >
> > To fix this just revalidate the clock comparator register with the
> > expected value.
> > In addition the special handling for udelay must be changed as well.
> >
> > Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> > Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
>
> [...]
>
> > ---
> > arch/s390/kernel/nmi.c | 10 ++++------
> > arch/s390/lib/delay.c | 14 +++++++++-----
> > 2 files changed, 13 insertions(+), 11 deletions(-)
> >
> > --- a/arch/s390/kernel/nmi.c
> > +++ b/arch/s390/kernel/nmi.c
> > @@ -95,7 +95,6 @@ EXPORT_SYMBOL_GPL(s390_handle_mcck);
> > static int notrace s390_revalidate_registers(struct mci *mci)
> > {
> > int kill_task;
> > - u64 tmpclock;
> > u64 zero;
> > void *fpt_save_area, *fpt_creg_save_area;
> >
> > @@ -214,11 +213,10 @@ static int notrace s390_revalidate_regis
> > : "0", "cc");
> > #endif
> > /* Revalidate clock comparator register */
> > - asm volatile(
> > - " stck 0(%1)\n"
> > - " sckc 0(%1)"
> > - : "=m" (tmpclock) : "a" (&(tmpclock)) : "cc", "memory");
> > -
> > + if (S390_lowcore.clock_comparator == -1)
> > + set_clock_comparator(S390_lowcore.mcck_clock);
> ^^^
> This line won't compile on 2.6.32. That's why I sent a slightly different
> patch to -stable (and also the reason why I removed Martin's Sign-off) ;)

Ah, please be more clear that you are sending a modifed version for me
to apply instead of taking the upstream patch directly, which is the
default for me to do so in order to make sure nothing is incorrect.

>
> Here is the version I sent to stable@kernel.org again:
>
> Subject: [S390] nmi: fix clock comparator revalidation

I'll go replace the version I had with this one.

thanks,

greg k-h


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