Re: Are BPF programs preemptible?

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On Mon, Jan 23, 2023 at 11:01 PM +02, Yaniv Agman wrote:
> ‫בתאריך יום ב׳, 23 בינו׳ 2023 ב-22:06 מאת ‪Martin KaFai Lau‬‏
> <‪martin.lau@xxxxxxxxx‬‏>:‬
>>
>> On 1/23/23 9:32 AM, Yaniv Agman wrote:
>> >>> interrupted the first one. But even then, I will need to find a way to
>> >>> know if my program currently interrupts the run of another program -
>> >>> is there a way to do that?
>> May be a percpu atomic counter to see if the bpf prog has been re-entered on the
>> same cpu.
>
> Not sure I understand how this will help. If I want to save local
> program data on a percpu map and I see that the counter is bigger then
> zero, should I ignore the event?

map_update w/ BPF_F_LOCK disables preemption, if you're after updating
an entry atomically. But it can't be used with PERCPU maps today.
Perhaps that's needed now too.




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