Re: rcu_read_lock() used illegally while idle!

[Steven Rostedt]

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().

-- Steve

> [53693.317485]  [<ffffffff8112d79f>] perf_ftrace_function_call+0xbf/0xd0
> [53693.318207]  [<ffffffff8110e1e1>] ? ftrace_ops_control_func+0x181/0x210
> [53693.318921]  [<ffffffff81074630>] ? __rcu_read_lock+0x20/0x20
> [53693.319621]  [<ffffffff81100cae>] ? rcu_eqs_enter_common+0x5e/0x470
> [53693.320330]  [<ffffffff8110e1e1>] ftrace_ops_control_func+0x181/0x210
> [53693.321046]  [<ffffffff816f4000>] ftrace_call+0x5/0x2f
> [53693.321763]  [<ffffffff8110e229>] ? ftrace_ops_control_func+0x1c9/0x210
> [53693.322490]  [<ffffffff816f4000>] ? ftrace_call+0x5/0x2f
> [53693.323221]  [<ffffffff81074635>] ? debug_lockdep_rcu_enabled+0x5/0x40
> [53693.323988]  [<ffffffff81074635>] ? debug_lockdep_rcu_enabled+0x5/0x40
> [53693.324728]  [<ffffffff81100cae>] ? rcu_eqs_enter_common+0x5e/0x470
> [53693.325489]  [<ffffffff8110112a>] rcu_eqs_enter+0x6a/0xb0
> [53693.326273]  [<ffffffff81103673>] rcu_user_enter+0x13/0x20
> [53693.327025]  [<ffffffff8114541a>] user_enter+0x6a/0xd0
> [53693.327783]  [<ffffffff8100f6d8>] syscall_trace_leave+0x78/0x140
> [53693.328551]  [<ffffffff816f46af>] int_check_syscall_exit_work+0x34/0x3d
>  


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