On Fri, Oct 13, 2023 at 7:00 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Fri, 13 Oct 2023 08:01:34 +0200 > Artem Savkov <asavkov@xxxxxxxxxx> wrote: > > > > But looking at [0] and briefly reading some of the discussions you, > > > Steven, had. I'm just wondering if it would be best to avoid > > > increasing struct trace_entry altogether? It seems like preempt_count > > > is actually a 4-bit field in trace context, so it doesn't seem like we > > > really need to allocate an entire byte for both preempt_count and > > > preempt_lazy_count. Why can't we just combine them and not waste 8 > > > extra bytes for each trace event in a ring buffer? > > > > > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?id=b1773eac3f29cbdcdfd16e0339f1a164066e9f71 > > > > I agree that avoiding increase in struct trace_entry size would be very > > desirable, but I have no knowledge whether rt developers had reasons to > > do it like this. > > > > Nevertheless I think the issue with verifier running against a wrong > > struct still needs to be addressed. > > Correct. My Ack is based on the current way things are done upstream. > It was just that linux-rt showed the issue, where the code was not as > robust as it should have been. To me this was a correctness issue, not > an issue that had to do with how things are done in linux-rt. I think we should at least add some BUILD_BUG_ON() that validates offsets in syscall_tp_t matches the ones in syscall_trace_enter and syscall_trace_exit, to fail more loudly if there is any mismatch in the future. WDYT? > > As for the changes in linux-rt, they are not upstream yet. I'll have my > comments on that code when that happens. Ah, ok, cool. I'd appreciate you cc'ing bpf@xxxxxxxxxxxxxxx in that discussion, thank you! > > -- Steve
