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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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