On Tue, Feb 18, 2020 at 12:46:09PM -0500, Steven Rostedt wrote:

On Tue, 18 Feb 2020 13:33:35 +0900
Masami Hiramatsu [off-list ref] wrote:

quoted

On Mon, 17 Feb 2020 08:31:12 -0800
"Paul E. McKenney" [off-list ref] wrote:

quoted

quoted

BTW, if you consider the x86 specific code is in the generic file,
we can move NOKPROBE_SYMBOL() in arch/x86/kernel/traps.c.
(Sorry, I've hit this idea right now)  

Might this affect other architectures with NMIs and probe-like things?
If so, it might make sense to leave it where it is.  

Yes, git grep shows that arm64 is using rcu_nmi_enter() in
debug_exception_enter().
OK, let's keep it, but maybe it is good to update the comment for
arm64 too. What about following?

+/*
+ * All functions in do_int3() on x86, do_debug_exception() on arm64 must be
+ * marked NOKPROBE before kprobes handler is called.
+ * ist_enter() on x86 and debug_exception_enter() on arm64 which is called
+ * before kprobes handle happens to call rcu_nmi_enter() which means
+ * that rcu_nmi_enter() must be marked NOKRPOBE.
+ */

Ah, why don't we just say...

/*
 * All functions called in the breakpoint trap handler (e.g. do_int3()
 * on x86), must not allow kprobes until the kprobe breakpoint handler
 * is called, otherwise it can cause an infinite recursion.
 * On some archs, rcu_nmi_enter() is called in the breakpoint handler
 * before the kprobe breakpoint handler is called, thus it must be
 * marked as NOKPROBE.
 */

And that way we don't make this an arch specific comment.

That looks good to me.  Masami, does this work for you?

							Thanx, Paul