[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20230123170753.7ac9419e@gandalf.local.home>
Date: Mon, 23 Jan 2023 17:07:53 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, will@...nel.org, boqun.feng@...il.com,
mark.rutland@....com, tglx@...utronix.de, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
seanjc@...gle.com, pbonzini@...hat.com, jgross@...e.com,
srivatsa@...il.mit.edu, amakhalov@...are.com,
pv-drivers@...are.com, mhiramat@...nel.org, wanpengli@...cent.com,
vkuznets@...hat.com, boris.ostrovsky@...cle.com, rafael@...nel.org,
daniel.lezcano@...aro.org, juri.lelli@...hat.com,
vincent.guittot@...aro.org, dietmar.eggemann@....com,
bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
vschneid@...hat.com, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
linux-trace-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 3/6] ftrace/x86: Warn and ignore graph tracing when RCU
is disabled
On Mon, 23 Jan 2023 16:53:04 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, 23 Jan 2023 21:50:12 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
>
> > All RCU disabled code should be noinstr and hence we should never get
> > here -- when we do, WARN about it and make sure to not actually do
> > tracing.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> > arch/x86/kernel/ftrace.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > --- a/arch/x86/kernel/ftrace.c
> > +++ b/arch/x86/kernel/ftrace.c
> > @@ -646,6 +646,9 @@ void prepare_ftrace_return(unsigned long
> > if (unlikely(atomic_read(¤t->tracing_graph_pause)))
> > return;
> >
> > + if (WARN_ONCE(!rcu_is_watching(), "RCU not on for: %pS\n", (void *)ip))
> > + return;
> > +
>
> Please add this to after recursion trylock below. Although WARN_ONCE()
> should not not have recursion issues, as function tracing can do weird
> things, I rather be safe than sorry, and not have the system triple boot
> due to some path that might get added in the future.
>
> If rcu_is_watching() is false, it will still get by the below recursion
> check and warn. That is, the below check should be done before this
> function calls any other function.
>
> > bit = ftrace_test_recursion_trylock(ip, *parent);
> > if (bit < 0)
> > return;
> >
>
Actually, perhaps we can just add this, and all you need to do is create
and set CONFIG_NO_RCU_TRACING (or some other name).
This should cover all ftrace locations. (Uncompiled).
-- Steve
diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
index c303f7a114e9..10ee3fbb9113 100644
--- a/include/linux/trace_recursion.h
+++ b/include/linux/trace_recursion.h
@@ -135,6 +135,22 @@ extern void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip);
# define do_ftrace_record_recursion(ip, pip) do { } while (0)
#endif
+#ifdef CONFIG_NO_RCU_TRACING
+# define trace_warn_on_no_rcu(ip) \
+ ({ \
+ bool __ret = false; \
+ if (!trace_recursion_test(TRACE_RECORD_RECURSION_BIT)) { \
+ trace_recursion_set(TRACE_RECORD_RECURSION_BIT); \
+ __ret = WARN_ONCE(!rcu_is_watching(), \
+ "RCU not on for: %pS\n", (void *)ip); \
+ trace_recursion_clear(TRACE_RECORD_RECURSION_BIT); \
+ } \
+ __ret; \
+ })
+#else
+# define trace_warn_on_no_rcu(ip) false
+#endif
+
/*
* Preemption is promised to be disabled when return bit >= 0.
*/
@@ -144,6 +160,9 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
unsigned int val = READ_ONCE(current->trace_recursion);
int bit;
+ if (trace_warn_on_no_rcu(ip))
+ return -1;
+
bit = trace_get_context_bit() + start;
if (unlikely(val & (1 << bit))) {
/*
Powered by blists - more mailing lists