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the >>> find_get_page() family return !uptodate pages. >>>=20 >>> But find_get_page() does not advertise itself as NMI-safe. And I >>> think it's wrong to try to make it NMI-safe. Most of the kernel is >>> not NMI-safe. I think it's incumbent on the BPF people to get the >>> information they need ahead of taking the NMI. NMI handlers are not >>> supposed to be doing a huge amount of work! I don't really understand >>> why it needs to do work in NMI context; surely it can note the location= of >>> the fault and queue work to be done later (eg on irq-enable, task-switc= h >>> or return-to-user) >>=20 >> The use case here is a profiler (similar to perf-record). Parsing the=20 >> build id in side the NMI makes the profiler a lot simpler. Otherwise,=20 >> we will need some post processing for each sample.=20 >=20 > Simpler for you, maybe. But this is an NMI! It's not supposed to > be doing printf-formatting or whatever, much less poking around > in the file cache. Like perf, it should record a sample and then > convert that later. Maybe it can defer to a tasklet, but i think > scheduling work is a better option. >=20 >> OTOH, it is totally fine if build_id_parse() fails some time, say < 5%.= =20 >> The profiler output is still useful in such cases.=20 >>=20 >> I guess the next step is to replace find_get_page() with a NMI-safe >> version? >=20 > No, absolutely not. Stop doing so much work in an NMI. While I understand the concern, it is not something we can easily remove,=20 as there are users rely on this feature. How about we discuss this at upcoming LSFMMBPF? Thanks, Song