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Date: Thu, 19 May 2011 16:47:43 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Yinghai Lu <yinghai@...nel.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40
On Wed, May 18, 2011 at 09:33:51PM -0700, Yinghai Lu wrote:
> ...
> [ 89.913205] ------------[ cut here ]------------
> [ 89.913216] WARNING: at kernel/rcutree.c:352 rcu_enter_nohz+0x49/0x8b()
> [ 89.913220] Hardware name: Sun Fire X4800 M2
> [ 89.913224] Modules linked in:
> [ 89.913230] Switched to NOHz mode on CPU #34
> [ 89.913237] Pid: 0, comm: swapper Tainted: G W 2.6.39-rc7-tip-yh-05281-g8e9254b-dirty #1019
> [ 89.913242] Call Trace:
> [ 89.913269] [<ffffffff81080144>] warn_slowpath_common+0x85/0x9d
> [ 89.913280] [<ffffffff81080176>] warn_slowpath_null+0x1a/0x1c
> [ 89.913290] [<ffffffff810d32cc>] rcu_enter_nohz+0x49/0x8b
> [ 89.913305] [<ffffffff810ab121>] tick_nohz_stop_sched_tick+0x27d/0x366
> [ 89.913317] [<ffffffff810391bc>] cpu_idle+0x7a/0xcc
> [ 89.913329] [<ffffffff81bda6e3>] rest_init+0xb7/0xbe
> [ 89.913340] [<ffffffff81bda62c>] ? csum_partial_copy_generic+0x16c/0x16c
> [ 89.913352] [<ffffffff82742e39>] start_kernel+0x3b2/0x3bd
> [ 89.913363] [<ffffffff827422cc>] x86_64_start_reservations+0x9c/0xa0
> [ 89.913374] [<ffffffff827424a8>] x86_64_start_kernel+0x1d8/0x1e3
> [ 89.913379] ---[ end trace a7919e7f17c0a726 ]---
> [ 89.913401] Dumping ftrace buffer:
> [ 89.913417] Switched to NOHz mode on CPU #4
> [ 89.913428] ---------------------------------
> [ 89.913444] Switched to NOHz mode on CPU #54
> [ 89.913467] CPU:0 [LOST 39120 EVENTS]
<snip>
> [ 89.918480] <idle>-0 0d... 89913074us : <stack trace>
> [ 89.918482] => rcu_irq_enter
> [ 89.918484] => irq_enter
> [ 89.918486] => smp_apic_timer_interrupt
> [ 89.918488] => apic_timer_interrupt
> [ 89.918489] => cpu_idle
> [ 89.918491] => rest_init
> [ 89.918492] => start_kernel
> [ 89.918494] => x86_64_start_reservations
> [ 89.918517] <idle>-0 0dN.. 89913130us : <stack trace>
> [ 89.918519] => rcu_irq_exit
> [ 89.918521] => irq_exit
> [ 89.918522] => smp_apic_timer_interrupt
> [ 89.918524] => apic_timer_interrupt
> [ 89.918526] => cpu_idle
> [ 89.918527] => rest_init
> [ 89.918529] => start_kernel
> [ 89.918530] => x86_64_start_reservations
> [ 89.918552] <idle>-0 0d... 89913196us : <stack trace>
> [ 89.918555] => rcu_enter_nohz
> [ 89.918556] => tick_nohz_stop_sched_tick
> [ 89.918558] => cpu_idle
> [ 89.918560] => rest_init
> [ 89.918561] => start_kernel
> [ 89.918563] => x86_64_start_reservations
> [ 89.918565] => x86_64_start_kernel
> [ 89.918569] ---------------------------------
So, the warning triggered there. But the pairing looks actually good,
given we had an interrupt right before that and it has called
irq_enter and irq_exit.
I have no clue about what happened there.
It may be easier if we have the value of dynticks and dynticks_nesting.
Can you please test the following branch?
git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
rcu/debug
It's Paul's branch + the early_initcall fix + the following patch:
---
commit 14667f347dea62d9e5a08e0f614840e50f73002c
Author: Frederic Weisbecker <fweisbec@...il.com>
Date: Thu May 19 16:25:19 2011 +0200
rcu: Trace dynticks internal values
To debug some nasty count bug.
Not-signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f30aea3..49d6348 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -349,6 +349,7 @@ void rcu_enter_nohz(void)
local_irq_save(flags);
trace_dump_stack();
rdtp = &__get_cpu_var(rcu_dynticks);
+ trace_printk("%x %x\n", atomic_read(&rdtp->dynticks), rdtp->dynticks_nesting);
if (WARN_ON_ONCE(rdtp->dynticks_nesting != 1))
ftrace_dump(DUMP_ORIG);
rdtp->dynticks_nesting = 1;
@@ -388,6 +389,7 @@ void rcu_exit_nohz(void)
local_irq_save(flags);
trace_dump_stack();
rdtp = &__get_cpu_var(rcu_dynticks);
+ trace_printk("%x %x\n", atomic_read(&rdtp->dynticks), rdtp->dynticks_nesting);
if (WARN_ON_ONCE(rdtp->dynticks_nesting != 0))
ftrace_dump(DUMP_ORIG);
rdtp->dynticks_nesting = 0;
@@ -463,9 +465,12 @@ void rcu_nmi_exit(void)
void rcu_irq_enter(void)
{
unsigned long flags;
+ struct rcu_dynticks *rdtp;
local_irq_save(flags);
trace_dump_stack();
+ rdtp = &__get_cpu_var(rcu_dynticks);
+ trace_printk("%x %x\n", atomic_read(&rdtp->dynticks), rdtp->dynticks_nesting);
__rcu_exit_nohz();
local_irq_restore(flags);
}
@@ -480,9 +485,12 @@ void rcu_irq_enter(void)
void rcu_irq_exit(void)
{
unsigned long flags;
+ struct rcu_dynticks *rdtp;
local_irq_save(flags);
trace_dump_stack();
+ rdtp = &__get_cpu_var(rcu_dynticks);
+ trace_printk("%x %x\n", atomic_read(&rdtp->dynticks), rdtp->dynticks_nesting);
__rcu_enter_nohz();
local_irq_restore(flags);
}
--
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