From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v3 05/22] rcu: Make RCU IRQ enter/exit functions rely on in_nmi() Date: Wed, 19 Feb 2020 09:42:11 -0800 Message-ID: <20200219174211.GL2935@paulmck-ThinkPad-P72> References: <20200219144724.800607165@infradead.org> <20200219150744.661923520@infradead.org> <20200219163156.GY2935@paulmck-ThinkPad-P72> <20200219163700.GK18400@hirez.programming.kicks-ass.net> <20200219170304.GG14946@hirez.programming.kicks-ass.net> Reply-To: paulmck@kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.29.99]:48352 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726518AbgBSRmM (ORCPT ); Wed, 19 Feb 2020 12:42:12 -0500 Content-Disposition: inline In-Reply-To: <20200219170304.GG14946@hirez.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org On Wed, Feb 19, 2020 at 06:03:04PM +0100, Peter Zijlstra wrote: > On Wed, Feb 19, 2020 at 05:37:00PM +0100, Peter Zijlstra wrote: > > On Wed, Feb 19, 2020 at 08:31:56AM -0800, Paul E. McKenney wrote: > > > > Here is the latest version of that comment, posted by Steve Rostedt. > > > > > > Thanx, Paul > > > > > > /* > > > * 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. > > > */ > > > > Oh right, let me stick that in a separate patch. Best we not loose that > > I suppose ;-) > > Having gone over the old thread, I ended up with the below. Anyone > holler if I got it wrong somehow. Looks good to me! Thanx, Paul > --- > Subject: rcu: Provide comment for NOKPROBE() on rcu_nmi_enter() > From: Steven Rostedt > > From: Steven Rostedt > > The rcu_nmi_enter() function was marked NOKPROBE() by commit > c13324a505c77 ("x86/kprobes: Prohibit probing on functions before > kprobe_int3_handler()") because the do_int3() call kprobe code must > not be invoked before kprobe_int3_handler() is called. It turns out > that ist_enter() (in do_int3()) calls rcu_nmi_enter(), hence the > marking NOKPROBE() being added to rcu_nmi_enter(). > > This commit therefore adds a comment documenting this line of > reasoning. > > Signed-off-by: Steven Rostedt > Reviewed-by: Masami Hiramatsu > Signed-off-by: Paul E. McKenney > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/rcu/tree.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -842,6 +842,14 @@ void rcu_nmi_enter(void) > { > rcu_nmi_enter_common(false); > } > +/* > + * 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. > + */ > NOKPROBE_SYMBOL(rcu_nmi_enter); > > /**