On Fri, Jun 21, 2024 at 10:57 PM Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > > On 2024/06/22 8:03, Axel Rasmussen wrote: > > No objections. Looking back all the way to the first version [1] the > > buffers were already percpu, instead of on the stack like this. IOW, > > there was no on-list discussion about why this shouldn't go on the > > stack. It has been a while, but if memory serves I opted to do it that > > way just out of paranoia around putting large buffers on the stack. > > But, I agree 256 bytes isn't all that large. > > > > That v1 patch wasn't all that complex, but then again it didn't deal > > with various edge cases properly :) so it has grown significantly more > > complex over time. Reconsidering the approach seems reasonable now, > > given how much code this removes. > > > > This change looks straightforwardly correct to me. You can take: > > > > Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > > Thank you. One question. CONTEXT_COUNT was defined as below. > > >> -/* > >> - * How many contexts our trace events might be called in: normal, softirq, irq, > >> - * and NMI. > >> - */ > >> -#define CONTEXT_COUNT 4 > > Is there possibility that this function (or in general, trace events) is called from NMI > context? If yes, I worry that functions called from get_mm_memcg_path() are not NMI-safe. > Original change at > https://lkml.kernel.org/r/3e9b2a54-73d4-48cb-a510-d17984c97a45@xxxxxxxxxxxxxxxxxxx was > posted due to worrying about NMI safety. I think it's unlikely, but I'm not certain. Although trace events *in general* can be called from NMI context. This code was added based on the discussion here [1] from v4 of this patchset. At the time I don't think we had any certainty that this *was* called from NMI context, but rather just that if CONTEXT_COUNT was 4 when it only had to be 3 in practice, it wasn't a huge deal, but getting it wrong the other way would be much worse. [1]: https://lore.kernel.org/r/20201020184746.300555-2-axelrasmussen@xxxxxxxxxx >
