Re: 4.19-rc1: ./include/linux/rcupdate.h:631 rcu_read_lock() used illegally while idle!

[Paul E. McKenney]

On Sat, Sep 01, 2018 at 06:45:31PM -0400, Steven Rostedt wrote:
> On Sat, 1 Sep 2018 10:54:42 -0700
> "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > On Sat, Sep 01, 2018 at 07:35:59PM +0200, Borislav Petkov wrote:
> > > This is a huge splat! It haz some perf* and sched* in it, I guess for
> > > peterz to stare at. And lemme add Paul for good measure too :)
> > > 
> > > Kernel is -rc1 + 3 microcode loader patches ontop which should not be
> > > related.  
> > 
> > It really is tracing from the idle loop.  But I thought that the event
> > tracing took care of that.  Adding Steve and Joel for their thoughts.
> > 
> > 							Thanx, Paul
> > 
> > > Thx.
> > > 
> > > ---
> > > [   62.409125] =============================
> > > [   62.409129] WARNING: suspicious RCU usage
> > > [   62.409133] 4.19.0-rc1+ #1 Not tainted
> > > [   62.409136] -----------------------------
> > > [   62.409140] ./include/linux/rcupdate.h:631 rcu_read_lock() used illegally while idle!
> > > [   62.409143] 
> > >                other info that might help us debug this:
> > > 
> > > [   62.409147] 
> > >                RCU used illegally from idle CPU!
> > >                rcu_scheduler_active = 2, debug_locks = 1
> > > [   62.409151] RCU used illegally from extended quiescent state!
> > > [   62.409155] 1 lock held by swapper/0/0:
> > > [   62.409158]  #0: 000000004557ee0e (rcu_read_lock){....}, at: perf_event_output_forward+0x0/0x130
> > > [   62.409175] 
> > >                stack backtrace:
> > > [   62.409180] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.19.0-rc1+ #1
> > > [   62.409183] Hardware name: LENOVO 2320CTO/2320CTO, BIOS G2ET86WW (2.06 ) 11/13/2012
> > > [   62.409187] Call Trace:
> > > [   62.409196]  dump_stack+0x85/0xcb
> > > [   62.409203]  perf_event_output_forward+0xf6/0x130
> 
> I think this is because we switched the trace point code to be
> protected by srcu instead of rcu_lock_sched() and a song and dance to
> "make RCU watch again" if it is not, but perf is using normal
> rcu_read_lock() internally even though it is hooked into the
> tracepoint code. Should perf switch to SRCU, or perhaps it can do the
> song and dance to make RCU watch again?

Well, this is a regression, so in theory we could push my three SRCU
patches into the current merge window, which would allow perf going
to SRCU, thus fixing the above splat.  I am OK either way.  What would
you prefer?

							Thanx, Paul

> -- Steve
> 
> 
> > > [   62.409215]  __perf_event_overflow+0x52/0xe0
> > > [   62.409223]  perf_swevent_overflow+0x91/0xb0
> > > [   62.409229]  perf_tp_event+0x11a/0x350
> > > [   62.409235]  ? find_held_lock+0x2d/0x90
> > > [   62.409251]  ? __lock_acquire+0x2ce/0x1350
> > > [   62.409263]  ? __lock_acquire+0x2ce/0x1350
> > > [   62.409270]  ? retint_kernel+0x2d/0x2d
> > > [   62.409278]  ? find_held_lock+0x2d/0x90
> > > [   62.409285]  ? tick_nohz_get_sleep_length+0x83/0xb0
> > > [   62.409299]  ? perf_trace_cpu+0xbb/0xd0
> > > [   62.409306]  ? perf_trace_buf_alloc+0x5a/0xa0
> > > [   62.409311]  perf_trace_cpu+0xbb/0xd0
> > > [   62.409323]  cpuidle_enter_state+0x185/0x340
> > > [   62.409332]  do_idle+0x1eb/0x260
> > > [   62.409340]  cpu_startup_entry+0x5f/0x70
> > > [   62.409347]  start_kernel+0x49b/0x4a6
> > > 
> > > [   62.409357]  secondary_startup_64+0xa4/0xb0
>