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

[George Anzinger <george@mvista.com>]

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/