Re: spin_lock error in arch/i386/kernel/time.c on APM resume

[George Anzinger <george@mvista.com>]

Zwane Mwaikambo wrote:
> On Sat, 12 Mar 2005, George Anzinger wrote:
> 
> 
>>Looks like we need the irq on the read clock also.  This is true both before
>>and  after the prior cmos_time changes.
>>
>>The attached replaces the patch I sent yesterday.
>>
>>For those wanting to fix the kernel with out those patches, all that is needed
>>its the chunk that applies, i.e. the _irq on the get_cmos_time() spinlocks.
>>
>>And more... That this occures implies we are attempting to update the cmos
>>clock on resume seems wrong.  One would presume that the time is wrong at this
>>time and we are about to save that wrong time.  Possibly the APM code should
>>change time_status to STA_UNSYNC on the way into the sleep (or what ever it is
>>called).  Who should we ping with this?
> 
> 
> timer_resume, which appears to be the problem, wants to calculate amount 
> of time was spent suspended, also your unconditional irq enable in 
> get_cmos_time breaks the atomicity of device_power_up and would deadlock 
> in sections of code which call get_time_diff() with xtime_lock held. I 
> sent a patch subject "APM: fix interrupts enabled in device_power_up" 
> which should address this.

I agree.  Still in all that follows, no one has addressed the apparent race 
described above.  The reason the system reported the errors that started this 
thread is that the APM restore code was trying to read the cmos clock (I assume 
to set the xtime clock) WHILE the timer interrupt code what trying to set the 
cmos clock from xtime.  In other words, it is destroying the time it is trying 
to read.  I repeat "Possibly the APM code should change time_status to 
STA_UNSYNC on the way into the sleep."  I am not sure how ntp is supposed to 
react to the resume but I suspect that the system time is rather out of sync...
-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/