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SubjectRe: 4.19-rc1: ./include/linux/rcupdate.h:631 rcu_read_lock() used illegally while idle!
On Tue, Sep 04, 2018 at 04:26:11PM -0400, Steven Rostedt wrote:
> On Sat, 1 Sep 2018 21:16:39 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > 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@linux.vnet.ibm.com> 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?
>
> I wonder if this partial revert will fix things?

I must defer to Borislav on this one. Assuming it has the desired
effect, I am good with it. Nicer and more contained fix than three
SRCU patches! ;-)

Thanx, Paul

> -- Steve
>
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 7f2e16e76ac4..041f7e56a289 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -158,8 +158,10 @@ extern void syscall_unregfunc(void);
> * For rcuidle callers, use srcu since sched-rcu \
> * doesn't work from the idle path. \
> */ \
> - if (rcuidle) \
> + if (rcuidle) { \
> idx = srcu_read_lock_notrace(&tracepoint_srcu); \
> + rcu_irq_enter_irqson(); \
> + } \
> \
> it_func_ptr = rcu_dereference_raw((tp)->funcs); \
> \
> @@ -171,8 +173,10 @@ extern void syscall_unregfunc(void);
> } while ((++it_func_ptr)->func); \
> } \
> \
> - if (rcuidle) \
> + if (rcuidle) { \
> + rcu_irq_exit_irqson(); \
> srcu_read_unlock_notrace(&tracepoint_srcu, idx);\
> + } \
> \
> preempt_enable_notrace(); \
> } while (0)
>

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