On Tue, 08 May 2018 15:41:11 +0530 "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> wrote: > Masami Hiramatsu wrote: > > On Mon, 07 May 2018 13:41:53 +0530 > > "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> wrote: > >> >> > >> >> I didn't understand that. Which code are you planning to remove? Can you > >> >> please elaborate? I thought we still need to disable preemption in the > >> >> ftrace handler. > >> > > >> > Yes, kprobe_ftrace_handler itself must be run under preempt disabled > >> > because it depends on a per-cpu variable. What I will remove is the > >> > redundant preempt disable/enable_noresched (unbalanced) pair in the > >> > kprobe_ftrace_handler, and jprobe x86 ports which is no more used. > >> > >> Won't that break out-of-tree users depending on returning a non-zero > >> value to handle preemption differently? You seem to have alluded to it > >> earlier in the mail chain above where you said that this is not just for > >> jprobes (though it was added for jprobes as the main use case). > > > > No, all users are in tree already (function override for bpf and error-injection). > > Ok, so BPF error injection is a new user that can return a non-zero > value from the pre handler. It looks like it can use KPROBES_ON_FTRACE > too. > > In that case, on function entry, we call into kprobe_ftrace_handler() > which will call fei_kprobe_handler(), which can re-enable premption > before returning 1. So, if you remove the additional > prempt_disable()/enable_no_resched() in kprobe_ftrace_handler(), then it > will become imbalanced, right? Right. So we have to fix both at once. Please check the patch below. https://patchwork.kernel.org/patch/10386171/ (Sorry, I missed to cc you...) > > > And also, for changing execution path by using kprobes, user handler must call > > not only preempt_enable(), but also clear current_kprobe per-cpu variable which > > is not exported to kmodules. > > Ok, good point. And that means we don't have any external users any > more. Yes :) Thank you, > > Thanks, > Naveen > > -- Masami Hiramatsu <mhiramat@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-trace-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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