Message-ID: <20120731120556.GB17252@localhost>
Date:	Tue, 31 Jul 2012 20:05:56 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Steven Rostedt <srostedt@...hat.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, rostedt@...dmis.org
Subject: Re: __update_max_tr: rcu_read_lock() used illegally while idle!

On Mon, Jul 30, 2012 at 11:39:12AM -0400, Steven Rostedt wrote:
> On Tue, 2012-07-24 at 17:03 +0800, Fengguang Wu wrote:
> > Hi Steven,
> 
> Hi Fengguang,
> 
> Just an FYI, It's best to send email to my rostedt@...dmis.org account.
> I don't check my redhat account every day.

OK, sorry for forgetting about that!

> > 
> > This looks like some old bug, so I directly report to you w/o trying
> > to bisect it. It only happens on the attached i386 randconfig and
> > happens in about half of the kvm boots.
> > 
> > [    1.380369] Testing tracer irqsoff: [    1.524917] 
> > [    1.525217] ===============================
> > [    1.525868] [ INFO: suspicious RCU usage. ]
> > [    1.526556] 3.5.0+ #1289 Not tainted
> > [    1.527124] -------------------------------
> > [    1.527799] /c/kernel-tests/src/linux/include/linux/rcupdate.h:730 rcu_read_lock() used illegally while idle!
> > [    1.529375] 
> > [    1.529375] other info that might help us debug this:
> > [    1.529375] 
> > [    1.530667] 
> > [    1.530667] RCU used illegally from idle CPU!
> > [    1.530667] rcu_scheduler_active = 1, debug_locks = 1
> > [    1.532383] RCU used illegally from extended quiescent state!
> > [    1.533297] 2 locks held by swapper/0/0:
> > 
> > [    1.533924]  #0: [    1.534271]  (max_trace_lock){......}, at: [<410e9d67>] check_critical_timing+0x67/0x1b0
> > [    1.534883]  #1:  (rcu_read_lock){.+.+..}, at: [<410e1ea0>] __update_max_tr+0x0/0x200
> > 
> > [    1.534883] stack backtrace:
> > [    1.534883] Pid: 0, comm: swapper/0 Not tainted 3.5.0+ #1289
> > [    1.534883] Call Trace:
> > [    1.534883]  [<41093a76>] lockdep_rcu_suspicious+0xc6/0x100
> > [    1.534883]  [<410e2071>] __update_max_tr+0x1d1/0x200
> 
> This is very weird because __update_max_tr does not use rcu_read lock().
> If you still have the kernel around (or can reproduce it), can you show
> the objdump of the __update_max_tr function. I wonder if some debug
> option requires RCU usage somewhere there.

Here is part of trace.s, where lockdep_rcu_suspicious shows up in 3
places:

.LFE2107:
	.size	tracing_record_cmdline, .-tracing_record_cmdline
	.section	.rodata.str1.1
.LC50:
	.string	"rcu_read_lock() used illegally while idle"
.LC51:
	.string	"/c/wfg/linux/include/linux/rcupdate.h"
.LC52:
	.string	"suspicious rcu_dereference_check() usage"
.LC53:
	.string	"rcu_read_unlock() used illegally while idle"
	.text
	.type	__update_max_tr, @function
__update_max_tr:
.LFB2091:
	.loc 4 661 0
	.cfi_startproc
.LVL1255:
.L796:
	pushl	%ebp	#
.LCFI356:
	.cfi_def_cfa_offset 8
	.cfi_offset 5, -8
	movl	%esp, %ebp	#,
.LCFI357:
	.cfi_def_cfa_register 5
	pushl	%edi	#
	pushl	%esi	#
	pushl	%ebx	#
	.cfi_offset 7, -12
	.cfi_offset 6, -16
	.cfi_offset 3, -20
	.loc 4 662 0
	leal	4(%ecx), %edi	#, tmp91
	.loc 4 661 0
	pushl	%ebx	#
	.loc 4 662 0
	movl	8(%eax,%edi,4), %esi	# tr_1(D)->data, data
.LVL1256:
	.loc 4 661 0
	movl	%edx, %ebx	# tsk, tsk
	.loc 4 665 0
	movl	%ecx, max_tr+4	# cpu, max_tr.cpu
	.loc 4 673 0
	movl	$4, %ecx	#, tmp102
.LVL1257:
	.loc 4 666 0
	movl	44(%esi), %eax	# data_3->preempt_timestamp, data_3->preempt_timestamp
.LVL1258:
	movl	48(%esi), %edx	# data_3->preempt_timestamp, data_3->preempt_timestamp
.LVL1259:
	movl	%eax, max_tr+12	# data_3->preempt_timestamp, max_tr.time_start
	.loc 4 669 0
	movl	tracing_max_latency, %eax	# tracing_max_latency, tracing_max_latency
	.loc 4 666 0
	movl	%edx, max_tr+16	# data_3->preempt_timestamp, max_tr.time_start
	.loc 4 668 0
	movl	max_tr+8(,%edi,4), %edi	# max_tr.data,
	.loc 4 669 0
	movl	%eax, 12(%edi)	# tracing_max_latency, max_data_5->saved_latency
	.loc 4 670 0
	movl	16(%esi), %eax	# data_3->critical_start, D.35758
	movl	%edi, %edx	#,
	.loc 4 668 0
	movl	%edi, -16(%ebp)	#, %sfp
.LVL1260:
	.loc 4 670 0
	movl	%eax, 16(%edi)	# D.35758, max_data_5->critical_start
	.loc 4 671 0
	movl	20(%esi), %eax	# data_3->critical_end, D.35759
	.loc 4 673 0
	leal	468(%ebx), %esi	#, tmp99
.LVL1261:
	.loc 4 671 0
	movl	%eax, 20(%edi)	# D.35759, max_data_5->critical_end
	.loc 4 673 0
	movl	%edi, %eax	# tmp1, tmp98
	addl	$60, %eax	#, tmp98
	movl	%eax, %edi	# tmp98, tmp100
	rep movsl
	.loc 4 674 0
	movl	248(%ebx), %eax	# tsk_9(D)->pid, D.35762
	movl	%eax, 52(%edx)	# D.35762, max_data_5->pid
.LBB1126:
.LBB1127:
.LBB1128:
	.file 20 "/c/wfg/linux/include/linux/rcupdate.h"
	.loc 20 721 0
	call	__rcu_read_lock	#
.LVL1262:
.LBB1129:
.LBB1130:
	.loc 20 276 0
	xorl	%ecx, %ecx	#
	xorl	%edx, %edx	#
	movl	$rcu_lock_map, %eax	#,
	pushl	$.L796	#
	pushl	$0	#
	pushl	$1	#
	pushl	$2	#
	call	lock_acquire	#
.LVL1263:
.LBE1130:
.LBE1129:
.LBB1131:
	.loc 20 724 0
	call	debug_lockdep_rcu_enabled	#
.LVL1264:
	addl	$16, %esp	#,
	testl	%eax, %eax	# D.38819
	je	.L798	#,
	cmpb	$0, __warned.7078	#, __warned
	jne	.L798	#,
	call	rcu_is_cpu_idle	#
.LVL1265:
	testl	%eax, %eax	# D.38816
	je	.L798	#,
	movl	$.LC50, %ecx	#,
	movl	$725, %edx	#,
	movl	$.LC51, %eax	#,
	movb	$1, __warned.7078	#, __warned
	call	lockdep_rcu_suspicious	#
.LVL1266:
.L798:
.LBE1131:
.LBE1128:
.LBE1127:
.LBB1132:
	.loc 4 675 0
	movl	460(%ebx), %esi	# tsk_9(D)->real_cred, _________p1
.LVL1267:
.LBB1133:
	call	debug_lockdep_rcu_enabled	#
.LVL1268:
	testl	%eax, %eax	# D.35763
	je	.L801	#,
	.loc 4 675 0 is_stmt 0 discriminator 1
	cmpb	$0, __warned.29430	#, __warned
	jne	.L801	#,
.LBB1134:
.LBB1135:
	.loc 20 311 0 is_stmt 1
	call	debug_lockdep_rcu_enabled	#
.LVL1269:
	testl	%eax, %eax	# D.38826
	je	.L801	#,
	.loc 20 313 0
	call	rcu_is_cpu_idle	#
.LVL1270:
	testl	%eax, %eax	# D.38824
	je	.L803	#,
.L804:
.LBE1135:
.LBE1134:
	.loc 4 675 0
	movl	$.LC52, %ecx	#,
	movl	$675, %edx	#,
	movl	$.LC25, %eax	#,
	movb	$1, __warned.29430	#, __warned
	call	lockdep_rcu_suspicious	#
.LVL1271:
	jmp	.L801	#
.L803:
.LBB1137:
.LBB1136:
	.loc 20 317 0
	movl	$rcu_lock_map, %eax	#,
	call	lock_is_held	#
.LVL1272:
.LBE1136:
.LBE1137:
	.loc 4 675 0
	testl	%eax, %eax	# D.38823
	je	.L804	#,
.L801:
.LBE1133:
.LBE1132:
	.loc 4 675 0 is_stmt 0 discriminator 2
	movl	4(%esi), %esi	# _________p1_13->uid, ___val
.LVL1273:
.LBB1138:
.LBB1139:
.LBB1140:
	.loc 20 745 0 is_stmt 1 discriminator 2
	call	debug_lockdep_rcu_enabled	#
.LVL1274:
	testl	%eax, %eax	# D.38830
	je	.L806	#,
	.loc 20 745 0 is_stmt 0
	cmpb	$0, __warned.7082	#, __warned
	jne	.L806	#,
	call	rcu_is_cpu_idle	#
.LVL1275:
	testl	%eax, %eax	# D.38827
	je	.L806	#,
	movl	$.LC53, %ecx	#,
	movl	$746, %edx	#,
	movl	$.LC51, %eax	#,
	movb	$1, __warned.7082	#, __warned
	call	lockdep_rcu_suspicious	#
.LVL1276:
.L806:
.LBE1140:
.LBB1141:
.LBB1142:
	.loc 20 281 0 is_stmt 1
	movl	$.L806, %ecx	#,
	movl	$1, %edx	#,
	movl	$rcu_lock_map, %eax	#,
	call	lock_release	#
.LVL1277:
.LBE1142:
.LBE1141:
	.loc 20 749 0
	call	__rcu_read_unlock	#
.LVL1278:
.LBE1139:
.LBE1138:
.LBE1126:
	.loc 4 675 0
	movl	-16(%ebp), %eax	# %sfp,
	.loc 4 676 0
	movl	-16(%ebp), %edx	# %sfp,
	.loc 4 675 0
	movl	%esi, 56(%eax)	# ___val, max_data_5->uid
	.loc 4 676 0
	movl	36(%ebx), %eax	# tsk_9(D)->static_prio, tmp103
	subl	$120, %eax	#, tmp103
	movl	%eax, 28(%edx)	# tmp103, max_data_5->nice
	.loc 4 677 0
	movl	148(%ebx), %eax	# tsk_9(D)->policy, D.35776
	movl	%eax, 32(%edx)	# D.35776, max_data_5->policy
	.loc 4 678 0
	movl	44(%ebx), %eax	# tsk_9(D)->rt_priority, D.35777
	movl	%eax, 36(%edx)	# D.35777, max_data_5->rt_priority
	.loc 4 681 0
	movl	%ebx, %eax	# tsk,
	call	tracing_record_cmdline	#
.LVL1279:
	.loc 4 682 0
	leal	-12(%ebp), %esp	#,
	popl	%ebx	#
	.cfi_restore 3
.LVL1280:
	popl	%esi	#
	.cfi_restore 6
.LVL1281:
	popl	%edi	#
	.cfi_restore 7
	popl	%ebp	#
.LCFI358:
	.cfi_restore 5
	.cfi_def_cfa 4, 4
	ret
	.cfi_endproc
.LFE2091:
--
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