Re: [PATCH] timers/migration: Fix livelock in tmigr_handle_remote_up()

[Thomas Gleixner <tglx@kernel.org>]

On Thu, Jun 04 2026 at 11:45, Frederic Weisbecker wrote:
> Le Wed, Jun 03, 2026 at 05:01:39PM +0000, Amit Matityahu a écrit :
>> Questions for maintainers:
>> 
>> 1. What was the original rationale for the cpu != smp_processor_id()
>>    check? There is no code comment, commit message explanation or anything
>>    in the original patch's email discussion as to why
>>    timer_expire_remote() is skipped for the local CPU.
>
> The rationale was about assuming that such an expired timerqueue actually
> reflected a timer that was handled locally already and so it could be safely
> discarded. So we could spare some locking.

Right, but the assumption would only be valid _if_ the jiffies value
which was used in run_timers(GLOBAL) is propagated into the remote
handling.

>> -	if (cpu != smp_processor_id())
>> -		timer_expire_remote(cpu);
>> +	timer_expire_remote(cpu);
>
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

I'll add a comment to that for posterity.