linux-kernel - Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH] kfence: Avoid stalling...)

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Message-ID: <20201120141639.3896a3c8@gandalf.local.home>
Date:   Fri, 20 Nov 2020 14:16:39 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Marco Elver <elver@...gle.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        kasan-dev <kasan-dev@...glegroups.com>, rcu@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: linux-next: stall warnings and deadlock on Arm64 (was: [PATCH]
 kfence: Avoid stalling...)

On Fri, 20 Nov 2020 19:17:37 +0100
Marco Elver <elver@...gle.com> wrote:

> > > +++ b/kernel/rcu/Makefile
> > > @@ -3,6 +3,13 @@
> > >  # and is generally not a function of system call inputs.
> > >  KCOV_INSTRUMENT := n
> > >  
> > > +ifdef CONFIG_FUNCTION_TRACER
> > > +CFLAGS_REMOVE_update.o = $(CC_FLAGS_FTRACE)
> > > +CFLAGS_REMOVE_sync.o = $(CC_FLAGS_FTRACE)
> > > +CFLAGS_REMOVE_srcutree.o = $(CC_FLAGS_FTRACE)
> > > +CFLAGS_REMOVE_tree.o = $(CC_FLAGS_FTRACE)
> > > +endif
> > > +  
> > 
> > Can you narrow it down further? That is, do you really need all of the
> > above to stop the stalls?  
> 
> I tried to reduce it to 1 or combinations of 2 files only, but that
> didn't work.

I'm curious if this would help at all?


diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2a52f42f64b6..d020ecefd151 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1094,7 +1094,7 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
  * if the current CPU is not in its idle loop or is in an interrupt or
  * NMI handler, return true.
  */
-bool rcu_is_watching(void)
+notrace bool rcu_is_watching(void)
 {
 	bool ret;
 
Although I don't see it in the recursion list.

-- Steve