linux-kernel - Re: rcu_read_lock() used illegally while idle!

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Date:	Thu, 23 May 2013 12:40:04 -0400
From:	Dave Jones <davej@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	paulmck@...ux.vnet.ibm.com,
	Linux Kernel <linux-kernel@...r.kernel.org>, fweisbec@...il.com
Subject: Re: rcu_read_lock() used illegally while idle!

On Wed, May 22, 2013 at 08:49:18AM -0400, Steven Rostedt wrote:

 > > ===============================
 > > [ INFO: suspicious RCU usage. ]
 > > 3.10.0-rc2+ #1 Not tainted
 > > -------------------------------
 > > include/linux/rcupdate.h:771 rcu_read_lock() used illegally while idle!
 > > other info that might help us debug this:
 > > RCU used illegally from idle CPU! rcu_scheduler_active = 1, debug_locks = 0
 > > RCU used illegally from extended quiescent state!
 > > 2 locks held by cc1/63645:
 > >  #0:  (&rq->lock){-.-.-.}, at: [<ffffffff816b39fd>] __schedule+0xed/0x9b0
 > >  #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff8109d645>] cpuacct_charge+0x5/0x1f0
 > > 
 > > CPU: 1 PID: 63645 Comm: cc1 Not tainted 3.10.0-rc2+ #1 [loadavg: 40.57 27.55 13.39 25/277 64369]
 > > Hardware name: Gigabyte Technology Co., Ltd. GA-MA78GM-S2H/GA-MA78GM-S2H, BIOS F12a 04/23/2010
 > >  0000000000000000 ffff88010f78fcf8 ffffffff816ae383 ffff88010f78fd28
 > >  ffffffff810b698d ffff88011c092548 000000000023d073 ffff88011c092500
 > >  0000000000000001 ffff88010f78fd60 ffffffff8109d7c5 ffffffff8109d645
 > > Call Trace:
 > >  [<ffffffff816ae383>] dump_stack+0x19/0x1b
 > >  [<ffffffff810b698d>] lockdep_rcu_suspicious+0xfd/0x130
 > >  [<ffffffff8109d7c5>] cpuacct_charge+0x185/0x1f0
 > >  [<ffffffff8109d645>] ? cpuacct_charge+0x5/0x1f0
 > >  [<ffffffff8108dffc>] update_curr+0xec/0x240
 > >  [<ffffffff8108f528>] put_prev_task_fair+0x228/0x480
 > >  [<ffffffff816b3a71>] __schedule+0x161/0x9b0
 > >  [<ffffffff816b4721>] preempt_schedule+0x51/0x80
 > >  [<ffffffff816b4800>] ? __cond_resched_softirq+0x60/0x60
 > >  [<ffffffff816b6824>] ? retint_careful+0x12/0x2e
 > >  [<ffffffff810ff3cc>] ftrace_ops_control_func+0x1dc/0x210
 > >  [<ffffffff816be280>] ftrace_call+0x5/0x2f
 > >  [<ffffffff816b681d>] ? retint_careful+0xb/0x2e
 > >  [<ffffffff816b4805>] ? schedule_user+0x5/0x70
 > >  [<ffffffff816b4805>] ? schedule_user+0x5/0x70
 > >  [<ffffffff816b6824>] ? retint_careful+0x12/0x2e
 > > ------------[ cut here ]------------
 > 
 > This looks to be the caused by the same issue that this patch fixes:
 > 
 > https://lkml.org/lkml/2013/5/10/537
 > 
 > The schedule_user() was traced, and the preempt_enable_no_trace() that
 > the function tracer does caused for a schedule to occur. As the
 > scheduler uses rcu, and it was called before schedule_user() could tell
 > the kernel that the context is changing from user to kernel.

That patch doesn't help unfortunatly.

	Dave

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