Re: rcu_read_lock() used illegally while idle!

[Jiri Olsa]

On Sat, May 25, 2013 at 02:20:04PM -0400, Steven Rostedt wrote:
> On Sat, 2013-05-25 at 09:59 -0400, Dave Jones wrote:
> > On Fri, May 24, 2013 at 03:23:40PM -0400, Steven Rostedt wrote:
> >  > On Fri, 2013-05-24 at 10:23 -0400, Dave Jones wrote:
> >  > 
> >  > > .config: http://paste.fedoraproject.org/14281/94052971/raw/
> >  > > 
> >  > > trace shows the problem process was 'cc1', so I was likely building a kernel
> >  > > at the time.  There was also a trinity run going on in the background.
> >  > > 
> >  > > cmdline: nothing special..
> >  > > 
> >  > > BOOT_IMAGE=/vmlinuz-3.10.0-rc2+ root=UUID=bee21cd9-1852-4d1d-9e9d-2e44332b8df1 ro rd.md=0 rd.lvm=0 rd.dm=0 vconsole.keymap=us rd.luks=0 vconsole.font=latarcyrheb-sun16 consoleblank=0 console=ttyUSB0,115200 console=tty0 pause_on_oops=30 audit=0
> >  > > 
> >  > 
> >  > OK, I'm able to reproduce this. Looks like the same issue happens from
> >  > other ways from userspace into the kernel (the next way was tracing
> >  > system calls).
> >  > 
> >  > Forget the other patch. Here's a new patch that is more specific to
> >  > tracing and context tracking.
> >  > 
> >  > Can you try this one out, please.
> > 
> > Took a lot longer to hit this..
> 
> This is a same but different bug ;-)
> 
> Looks like we fixed all the function tracing infrastructure problems,
> but this is a function tracer user problem. Namely perf.
> 
> > 
> > [53693.297516] ===============================
> > [53693.298109] [ INFO: suspicious RCU usage. ]
> > [53693.298562] 3.10.0-rc2+ #38 Not tainted
> > [53693.299017] -------------------------------
> > [53693.299474] include/linux/rcupdate.h:771 rcu_read_lock() used illegally while idle!
> > [53693.299959] 
> > other info that might help us debug this:
> > 
> > [53693.301420] 
> > RCU used illegally from idle CPU!
> > rcu_scheduler_active = 1, debug_locks = 0
> > [53693.302918] RCU used illegally from extended quiescent state!
> > [53693.303462] 1 lock held by trinity-child1/18786:
> > [53693.303966]  #0:  (rcu_read_lock){.+.+..}, at: [<ffffffff8113dd48>] __perf_event_overflow+0x108/0x310
> > [53693.304557] 
> > stack backtrace:
> > [53693.305608] CPU: 3 PID: 18786 Comm: trinity-child1 Not tainted 3.10.0-rc2+ #38 
> > [53693.306790]  0000000000000000 ffff88020767bac8 ffffffff816e2f6b ffff88020767baf8
> > [53693.307408]  ffffffff810b5897 ffff88021de92520 0000000000000000 ffff88020767bbf8
> > [53693.308035]  0000000000000000 ffff88020767bb78 ffffffff8113ded4 ffffffff8113dd48
> > [53693.308671] Call Trace:
> > [53693.309301]  [<ffffffff816e2f6b>] dump_stack+0x19/0x1b
> > [53693.309943]  [<ffffffff810b5897>] lockdep_rcu_suspicious+0xe7/0x120
> > [53693.310596]  [<ffffffff8113ded4>] __perf_event_overflow+0x294/0x310
> > [53693.311256]  [<ffffffff8113dd48>] ? __perf_event_overflow+0x108/0x310
> > [53693.311923]  [<ffffffff81309289>] ? __const_udelay+0x29/0x30
> > [53693.312596]  [<ffffffff81076054>] ? __rcu_read_unlock+0x54/0xa0
> > [53693.313275]  [<ffffffff816f4000>] ? ftrace_call+0x5/0x2f
> > [53693.313958]  [<ffffffff8113dfa1>] perf_swevent_overflow+0x51/0xe0
> > [53693.314650]  [<ffffffff8113e08f>] perf_swevent_event+0x5f/0x90
> > [53693.315347]  [<ffffffff8113e1c9>] perf_tp_event+0x109/0x4f0
> > [53693.316059]  [<ffffffff8113e36f>] ? perf_tp_event+0x2af/0x4f0
> > [53693.316773]  [<ffffffff81074630>] ? __rcu_read_lock+0x20/0x20
> 
> Ouch! perf function tracing uses rcu_lock(). This should be avoided.
> Believe it or not, rcu_lock() is too invasive for function tracing, not
> to mention that the function tracer traces rcu_lock().
> 
> Jiri,
> 
> Is there a way you can make perf not use rcu here? Or we need to
> blacklist what perf can trace. It can not trace any rcu calls. Here it
> looks like it traced rcu_eqs_enter(). It also wont be able to trace
> anything before user_exit() or after user_enter().

ok, I'll check

jirka
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