On Thu, 20 Aug 2020 19:20:46 +0200
Marco Elver <el...@google.com> wrote:
> On Thu, Aug 20, 2020 at 04:58PM +0200, pet...@infradead.org wrote:
> > On Thu, Aug 20, 2020 at 10:36:43AM -0400, Steven Rostedt wrote:
> > >
> > > I tested this series on top of tip/master and triggered the below
> > > warning when running the irqsoff tracer boot up test (config attached).
> > >
> > > -- Steve
> > >
> > > Testing tracer irqsoff:
> > >
> > > =============================
> > > WARNING: suspicious RCU usage
> > > 5.9.0-rc1-test+ #92 Not tainted
> > > -----------------------------
> > > include/trace/events/lock.h:13 suspicious rcu_dereference_check() usage!
> > >
> ...
> >
> > Shiny, I think that wants something like the below, but let me go frob
> > my config and test it.
> >
> > ---
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> ...
>
> With that applied (manually, due to conflicts), I still get warnings for
> certain call locations with KCSAN on (that is with my fix from the other
> email):
>
> | =============================
> | WARNING: suspicious RCU usage
> | 5.9.0-rc1+ #23 Tainted: G W
> | -----------------------------
> | include/trace/events/random.h:310 suspicious rcu_dereference_check() usage!
> |
> | other info that might help us debug this:
> |
> |
> | rcu_scheduler_active = 2, debug_locks = 0
> | RCU used illegally from extended quiescent state!
> | no locks held by swapper/1/0.
> |
> | stack backtrace:
> | CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W 5.9.0-rc1+ #23
> | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1
> 04/01/2014
> | Call Trace:
> | __dump_stack lib/dump_stack.c:77 [inline]
> | dump_stack+0xf1/0x14d lib/dump_stack.c:118
> | trace_prandom_u32 include/trace/events/random.h:310 [inline]
> | prandom_u32+0x1ee/0x200 lib/random32.c:86
> | prandom_u32_max include/linux/prandom.h:46 [inline]
> | reset_kcsan_skip kernel/kcsan/core.c:277 [inline]
> | kcsan_setup_watchpoint+0x9b/0x600 kernel/kcsan/core.c:424
> | is_idle_task+0xd/0x20 include/linux/sched.h:1671 <==== inline,
> but not noinstr
> | irqentry_enter+0x17/0x50 kernel/entry/common.c:293 <====
> noinstr function
>
What happens if you apply the below patch?
-- Steve
diff --git a/lib/random32.c b/lib/random32.c
index 932345323af0..1c5607a411d4 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -83,7 +83,7 @@ u32 prandom_u32(void)
u32 res;
res = prandom_u32_state(state);
- trace_prandom_u32(res);
+ trace_prandom_u32_rcuidle(res);
put_cpu_var(net_rand_state);
return res;
