Masami Hiramatsu wrote:
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/
Ah, so your intent was to change the semantics of how the pre handler works! I missed that aspect. This now makes sense. Thanks for the clarification.
- Naveen -- 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
|