Re: [PATCH] clean up FIXME in do_timer_interrupt-lock fix

[George Anzinger]

Andrew Morton wrote:
> George Anzinger <george@xxxxxxxxxx> wrote:
>
> > Did you pick this up?  First sent on 3-11.
>
>
> I did, although now looking at it I have issues.
>
>
> > I was not happy with the locking on this.  Two changes:
> > 1) Turn off irq while setting the clock.
> > 2) Call the timer code only through the timer interface 
> >    (set a short timer to do it from the ntp call).
I wanted the calls to sync_cmos_clock() to be made in a consistent environment. 
 This was not true when calling it directly from the NTP call code.  The change 
means that sync_cmos_clock() is ALWAYS called from run_timers(), i.e. as a timer 
call back function.
> I would consider this to be an inadequate description :(
>
>
> > Signed-off-by: George Anzinger <george@xxxxxxxxxx>
> >
> >  time.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> >
> > Index: linux-2.6.12-rc/arch/i386/kernel/time.c
> > ===================================================================
> > --- linux-2.6.12-rc.orig/arch/i386/kernel/time.c
> > +++ linux-2.6.12-rc/arch/i386/kernel/time.c
> > @@ -176,12 +176,12 @@ static int set_rtc_mmss(unsigned long no
> >  	int retval;
> >  
> >  	/* gets recalled with irq locally disabled */
> > -	spin_lock(&rtc_lock);
> > +	spin_lock_irq(&rtc_lock);
> >  	if (efi_enabled)
> >  		retval = efi_set_rtc_mmss(nowtime);
> >  	else
> >  		retval = mach_set_rtc_mmss(nowtime);
> > -	spin_unlock(&rtc_lock);
> > +	spin_unlock_irq(&rtc_lock);
> >  
> >  	return retval;
> >  }
>
>
> If the comment is correct, and this code is called with local irq's
> disabled then this patch should be using spin_lock_irqsave()

With the change below, it is always called from the timer call back code which, 
I believe, is always called with irq on.  Looks like I missed the comment :(
> > @@ -338,7 +338,7 @@ static void sync_cmos_clock(unsigned lon
> >  }
> >  void notify_arch_cmos_timer(void)
> >  {
> > -	sync_cmos_clock(0);
> > +	mod_timer(&sync_cmos_timer, jiffies + 1);
> >  }
> >  static long clock_cmos_diff, sleep_start;
> >  
>
>
> Your description says what this does, but it doesn't way why it was done?

--
George Anzinger   george@xxxxxxxxxx
High-res-timers:  http://sourceforge.net/projects/high-res-timers/

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