Re: Warning/trace in kernel/smp.c:815 smp_call_function_many_cond

[Thomas Gleixner]

On Mon, Feb 24 2025 at 06:57, Paul E. McKenney wrote:

> On Mon, Feb 24, 2025 at 02:57:40PM +0100, Christian Heusel wrote:
>> Hello everyone,
>> 
>> I have noticed the following new warning in my dmesg output, I think I
>> have first seen this when upgrading to v6.14-rc1.
>> 
>> So far I have been unsuccessfull in bisecting it, therefore it would be
>> nice to get some input whether this is something serious or how I could
>> debug it further. I have also attached a full dmesg for more context.
>> 
>>     ------------[ cut here ]------------
>>     WARNING: CPU: 3 PID: 0 at kernel/smp.c:815 smp_call_function_many_cond+0x46b/0x4c0
>
> This happens when something invokes one of the smp_call_function()
> APIs not in task context, that is, if it is called from NMI, hard IRQ,
> or soft IRQ contexts.
>
> Which it is in this case, due to clocksource_watchdog() being invoked
> from a timer handler.  This only matters if the clocksource is being
> marked unstable, which is what you are seeing.
>
> One possible fix is to move the call to cs->mark_unstable(cs) from
> __clocksource_unstable() to clocksource_watchdog_work().  This would
> require marking the clocksource so that clocksource_watchdog_work()
> could find it.
>
> But is there a better way?

That's fine and should be trivial to do. This business is asynchronous
anyway, so it does not matter much when the unstable call is a bit
delayed.

Thanks,

        tglx