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

George Anzinger
2005-03-19T22:24:10Z

Andrew Morton wrote:
> George Anzinger <george@mvista.com> 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@mvista.com>
>>
>> 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@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/