Re: [PATCH] x86: fix locking and sync bugs in x86_64 RTC code in time_64.c

["David P. Reed" <dpreed@reed.com>]

Will make two patches and resend.

Thomas Gleixner wrote:
> David,
>
> On Mon, 12 Nov 2007, David P. Reed wrote:
>
>   
> > From: David P. Reed
> >
> > Fix two bugs in arch/x86/kernel/time_64.c that affect the x86_64 kernel. 1) a
> > repeatable hard freeze due to interrupts when the ntpd service calls
> > update_persistent_clock(), 2) potentially unstable PC RTC timer values when
> > timer is read.
> >     
>
> 1) Please send separate patches for separate problems.
>
> 2) Your patch is white space damaged and does not apply. Please run it
>    through scripts/checkpatch.pl before submitting, maybe send it to
>    yourself first and verify that it applies correctly.
>
>   
> > Signed-off-by: David P. Reed <dpreed@reed.com>
> > ---
> > More explanation:
> > 1) A repeatable but randomly timed freeze has been happening in Fedora 6 and 7
> > for the last year, whenever I run the ntpd service on my AMD64x2 HP Pavilion
> > dv9000z laptop.  This freeze is due to the use of spin_lock(&rtc_lock) under
> > the assumption (per a bad comment) that set_rtc_mmss is called only with
> > interrupts disabled.  The call from ntp.c to update_persistent_clock is made
> > with interrupts enabled.
> >     
>
> Good catch.
>  
>   
> > 2) the use of an incorrect technique for reading the standard PC RTC timer,
> > which is documented to "disconnect" time registers from the bus while updates
> > are in progress.  The use of UIP flag while interrupts are disabled to protect
> > a 244 microsecond window is one of the Motorola spec sheet's documented ways
> > to read the RTC time registers reliably.  I realize that not all "clones" of
> > the
> >     
>
> of the what ?
>
> Also put the detailed description into the patch comment, please.
>
>   
> > The patch updates the misleading comments and minimizes the amount of time
> > that the kernel disables interrupts.
> >
> > I have thoroughly tested this patch on a number of x86_64 machines with
> > various numbers of cores and chipsets, using 2.6.24rc2 kernel source. Note
> > that while testing the ntp code I found another bug in kernel/time/ntp.c which
> > is independent of this fix - neither patch requires the other.
> >
> > If possible, I'd love to see the patch merged with 2.6.24, and even with
> > 2.6.23.
> >     
>
> Care to resend ?
>
> Thanks,
>
>      tglx
>
>   
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