[BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Li Zefan]

While running a ftrace test, a kernel warning showed up. The bug is not so
easy to reproduce, normally it takes 30 mins to 2 hours.

After revering 3c05d7482777f15e71bb4cb1ba78dee2800dfec6, I ran the test
for 15 hours, and the bug seems disapeared.

------------[ cut here ]------------
WARNING: at kernel/trace/ring_buffer.c:3420 ring_buffer_reset_cpu+0x5a/0x9c()
Hardware name: PRIMERGY                      
Modules linked in: ipt_MASQUERADE iptable_nat nf_nat bridge stp llc deflate zlib_deflate ctr camellia cast5 rmd160 crypto_null ccm serpent blowfish twofish_x86_64 twofish_common ecb xcbc cbc sha256_generic sha512_generic des_generic cryptd aes_x86_64 aes_generic ah6 ah4 esp6 esp4 xfrm4_mode_beet xfrm4_tunnel tunnel4 xfrm4_mode_tunnel xfrm4_mode_transport xfrm6_mode_transport xfrm6_mode_beet ipcomp ipcomp6 xfrm_ipcomp xfrm6_tunnel tunnel6 af_key autofs4 sunrpc ipv6 dm_mirror dm_region_hash dm_log dm_multipath uinput i5k_amb hwmon e1000e i5000_edac edac_core iTCO_wdt iTCO_vendor_support shpchp i2c_i801 i2c_core serio_raw pcspkr pata_acpi ata_generic mptsas mptscsih ata_piix mptbase scsi_transport_sas dm_mod [last unloaded: speedstep_lib]
Pid: 2108, comm: ftrace_current_ Tainted: G        W  2.6.33-tip+ #2
Call Trace:
 [<ffffffff8104ebd0>] warn_slowpath_common+0x7c/0x94
 [<ffffffff8104ebfc>] warn_slowpath_null+0x14/0x16
 [<ffffffff810a50f5>] ring_buffer_reset_cpu+0x5a/0x9c
 [<ffffffff810aa3f0>] tracing_reset_online_cpus+0x4a/0x79
 [<ffffffff810aa434>] tracer_init+0x15/0x20
 [<ffffffff810aa601>] tracing_set_tracer+0x1c2/0x1e7
 [<ffffffff810d9847>] ? might_fault+0x5c/0xac
 [<ffffffff810aa6b2>] tracing_set_trace_write+0x8c/0xbc
 [<ffffffff810a8e79>] ? trace_buffer_lock_reserve+0x21/0x56
 [<ffffffff810a95ce>] ? trace_current_buffer_lock_reserve+0x16/0x18
 [<ffffffff813ef135>] ? retint_swapgs+0x13/0x1b
 [<ffffffff81104618>] vfs_write+0xae/0x10b
 [<ffffffff81104735>] sys_write+0x4a/0x6e
 [<ffffffff81009da6>] tracesys+0xd0/0xd5
---[ end trace f7002f0890d5b023 ]---

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Lai Jiangshan]

Li Zefan wrote:
> While running a ftrace test, a kernel warning showed up. The bug is not so
> easy to reproduce, normally it takes 30 mins to 2 hours.
> 
> After revering 3c05d7482777f15e71bb4cb1ba78dee2800dfec6, I ran the test
> for 15 hours, and the bug seems disapeared.
> 

This bug exhausted us, we found a issue: a tiny window which is
one of causes of this bug. This patch is to close this tiny window.
(bug is not fixed)

From: Lai Jiangshan <laijs@cn.fujitsu.com>

ringbuffer resizing and reseting will increase the ->record_disabled
and then wait until a rcu_shced grace period passes.

Contrarily, testing ->record_disabled should be at the same
preempt disabled critical region as writing into ringbuffer, otherwise
it will leave a window break ringbuffer resizing or reseting.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reported-by: Li Zefan <lizf@cn.fujitsu.com>
---
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 8c1b2d2..54191d6 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2232,12 +2232,12 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
 	if (ring_buffer_flags != RB_BUFFERS_ON)
 		return NULL;
 
-	if (atomic_read(&buffer->record_disabled))
-		return NULL;
-
 	/* If we are tracing schedule, we don't want to recurse */
 	resched = ftrace_preempt_disable();
 
+	if (atomic_read(&buffer->record_disabled))
+		goto out_nocheck;
+
 	if (trace_recursive_lock())
 		goto out_nocheck;
 
@@ -2469,11 +2469,11 @@ int ring_buffer_write(struct ring_buffer *buffer,
 	if (ring_buffer_flags != RB_BUFFERS_ON)
 		return -EBUSY;
 
-	if (atomic_read(&buffer->record_disabled))
-		return -EBUSY;
-
 	resched = ftrace_preempt_disable();
 
+	if (atomic_read(&buffer->record_disabled))
+		goto out;
+
 	cpu = raw_smp_processor_id();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Steven Rostedt]

On Mon, 2010-03-08 at 14:50 +0800, Lai Jiangshan wrote:
> Li Zefan wrote:
> > While running a ftrace test, a kernel warning showed up. The bug is not so
> > easy to reproduce, normally it takes 30 mins to 2 hours.
> > 
> > After revering 3c05d7482777f15e71bb4cb1ba78dee2800dfec6, I ran the test
> > for 15 hours, and the bug seems disapeared.
> > 
> 
> This bug exhausted us, we found a issue: a tiny window which is
> one of causes of this bug. This patch is to close this tiny window.
> (bug is not fixed)
> 
> From: Lai Jiangshan <laijs@cn.fujitsu.com>
> 
> ringbuffer resizing and reseting will increase the ->record_disabled
> and then wait until a rcu_shced grace period passes.
> 
> Contrarily, testing ->record_disabled should be at the same
> preempt disabled critical region as writing into ringbuffer, otherwise
> it will leave a window break ringbuffer resizing or reseting.

So the resizing and the resetting need a synchronize_sched() after the
disabling of the buffers, right?

-- Steve

> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> Reported-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 8c1b2d2..54191d6 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -2232,12 +2232,12 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
>  	if (ring_buffer_flags != RB_BUFFERS_ON)
>  		return NULL;
>  
> -	if (atomic_read(&buffer->record_disabled))
> -		return NULL;
> -
>  	/* If we are tracing schedule, we don't want to recurse */
>  	resched = ftrace_preempt_disable();
>  
> +	if (atomic_read(&buffer->record_disabled))
> +		goto out_nocheck;
> +
>  	if (trace_recursive_lock())
>  		goto out_nocheck;
>  
> @@ -2469,11 +2469,11 @@ int ring_buffer_write(struct ring_buffer *buffer,
>  	if (ring_buffer_flags != RB_BUFFERS_ON)
>  		return -EBUSY;
>  
> -	if (atomic_read(&buffer->record_disabled))
> -		return -EBUSY;
> -
>  	resched = ftrace_preempt_disable();
>  
> +	if (atomic_read(&buffer->record_disabled))
> +		goto out;
> +
>  	cpu = raw_smp_processor_id();
>  
>  	if (!cpumask_test_cpu(cpu, buffer->cpumask))
> 
> 

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Steven Rostedt]

On Mon, 2010-03-08 at 10:03 -0500, Steven Rostedt wrote:

> > ringbuffer resizing and reseting will increase the ->record_disabled
> > and then wait until a rcu_shced grace period passes.
> > 
> > Contrarily, testing ->record_disabled should be at the same
> > preempt disabled critical region as writing into ringbuffer, otherwise
> > it will leave a window break ringbuffer resizing or reseting.
> 
> So the resizing and the resetting need a synchronize_sched() after the
> disabling of the buffers, right?

Looking at the code, the synchronize_sched() is already done in
ring_buffer_resize, and the caller (trace.c:tracing_reset() ) also
disables the ring buffer and calls synchronize_sched().

With that, what other window is still opened (after this fix)?

-- Steve

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Lai Jiangshan]

Steven Rostedt wrote:
> On Mon, 2010-03-08 at 10:03 -0500, Steven Rostedt wrote:
> 
>>> ringbuffer resizing and reseting will increase the ->record_disabled
>>> and then wait until a rcu_shced grace period passes.
>>>
>>> Contrarily, testing ->record_disabled should be at the same
>>> preempt disabled critical region as writing into ringbuffer, otherwise
>>> it will leave a window break ringbuffer resizing or reseting.
>> So the resizing and the resetting need a synchronize_sched() after the
>> disabling of the buffers, right?
> 
> Looking at the code, the synchronize_sched() is already done in
> ring_buffer_resize, and the caller (trace.c:tracing_reset() ) also
> disables the ring buffer and calls synchronize_sched().
> 
> With that, what other window is still opened (after this fix)?
> 

This window is still opened: (RCU vs IDLE vs Tracing)

synchronize_sched() does not protect preempt_disable()/enable() for
idle process. But tracing(function_graph, function) introduce more
preempt_disable()/enable() for idle process. It brings windows.

I bet that this bug is not come from this window.
(I added some strict code to RCU and did stress test,
bug was still occurred.)

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Steven Rostedt]

On Tue, 2010-03-09 at 11:35 +0800, Lai Jiangshan wrote:
> Steven Rostedt wrote:
> > On Mon, 2010-03-08 at 10:03 -0500, Steven Rostedt wrote:
> > 
> >>> ringbuffer resizing and reseting will increase the ->record_disabled
> >>> and then wait until a rcu_shced grace period passes.
> >>>
> >>> Contrarily, testing ->record_disabled should be at the same
> >>> preempt disabled critical region as writing into ringbuffer, otherwise
> >>> it will leave a window break ringbuffer resizing or reseting.
> >> So the resizing and the resetting need a synchronize_sched() after the
> >> disabling of the buffers, right?
> > 
> > Looking at the code, the synchronize_sched() is already done in
> > ring_buffer_resize, and the caller (trace.c:tracing_reset() ) also
> > disables the ring buffer and calls synchronize_sched().
> > 
> > With that, what other window is still opened (after this fix)?
> > 
> 
> This window is still opened: (RCU vs IDLE vs Tracing)
> 
> synchronize_sched() does not protect preempt_disable()/enable() for
> idle process. But tracing(function_graph, function) introduce more
> preempt_disable()/enable() for idle process. It brings windows.

It most definitely should. If it does not, then we have major problems.
>From the comment above synchronize_sched(void):

/**
 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
 *
 * Control will return to the caller some time after a full rcu-sched
 * grace period has elapsed, in other words after all currently executing
 * rcu-sched read-side critical sections have completed.   These read-side
 * critical sections are delimited by rcu_read_lock_sched() and
 * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
 * local_irq_disable(), and so on may be used in place of
 * rcu_read_lock_sched().

I do not see how idle can be ignored here.

> 
> I bet that this bug is not come from this window.
> (I added some strict code to RCU and did stress test,
> bug was still occurred.)
> 

What exactly were you doing when this happened? Was this from Li's test?

-- Steve

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Steven Rostedt]

On Tue, 2010-03-09 at 11:35 +0800, Lai Jiangshan wrote:
> Steven Rostedt wrote:
> > On Mon, 2010-03-08 at 10:03 -0500, Steven Rostedt wrote:
> > 
> >>> ringbuffer resizing and reseting will increase the ->record_disabled
> >>> and then wait until a rcu_shced grace period passes.
> >>>
> >>> Contrarily, testing ->record_disabled should be at the same
> >>> preempt disabled critical region as writing into ringbuffer, otherwise
> >>> it will leave a window break ringbuffer resizing or reseting.
> >> So the resizing and the resetting need a synchronize_sched() after the
> >> disabling of the buffers, right?
> > 
> > Looking at the code, the synchronize_sched() is already done in
> > ring_buffer_resize, and the caller (trace.c:tracing_reset() ) also
> > disables the ring buffer and calls synchronize_sched().
> > 
> > With that, what other window is still opened (after this fix)?
> > 
> 
> This window is still opened: (RCU vs IDLE vs Tracing)
> 
> synchronize_sched() does not protect preempt_disable()/enable() for
> idle process. But tracing(function_graph, function) introduce more
> preempt_disable()/enable() for idle process. It brings windows.
> 
> I bet that this bug is not come from this window.
> (I added some strict code to RCU and did stress test,
> bug was still occurred.)

With Li's test, I was able to trigger the ring_buffer warning about
resetting while committing. I was still able to trigger it with your
patch to move the ring buffer disable code. But I did not trigger it
with both the ring buffer disable code _and_ your RCU fix.

But I was able to trigger the segfault that Li is seeing. That is most
likely a separate issue. I'm currently writing special debug code to
find out why that is happening.

Thanks!

-- Steve

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Steven Rostedt]

On Tue, 2010-03-09 at 12:28 -0500, Steven Rostedt wrote:
> On Tue, 2010-03-09 at 11:35 +0800, Lai Jiangshan wrote:

> With Li's test, I was able to trigger the ring_buffer warning about
> resetting while committing. I was still able to trigger it with your
> patch to move the ring buffer disable code. But I did not trigger it
> with both the ring buffer disable code _and_ your RCU fix.

Spoke too soon. I hit it again. But I think I know why.

-- Steve

[tip:tracing/urgent] ring-buffer: Move disabled check into preempt disable section

[tip-bot for Lai Jiangshan]

Commit-ID:  52fbe9cde7fdb5c6fac196d7ebd2d92d05ef3cd4
Gitweb:     http://git.kernel.org/tip/52fbe9cde7fdb5c6fac196d7ebd2d92d05ef3cd4
Author:     Lai Jiangshan <laijs@cn.fujitsu.com>
AuthorDate: Mon, 8 Mar 2010 14:50:43 +0800
Committer:  Steven Rostedt <rostedt@goodmis.org>
CommitDate: Fri, 12 Mar 2010 20:26:56 -0500

ring-buffer: Move disabled check into preempt disable section

The ring buffer resizing and resetting relies on a schedule RCU
action. The buffers are disabled, a synchronize_sched() is called
and then the resize or reset takes place.

But this only works if the disabling of the buffers are within the
preempt disabled section, otherwise a window exists that the buffers
can be written to while a reset or resize takes place.

Cc: stable@kernel.org
Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4B949E43.2010906@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 8c1b2d2..54191d6 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2232,12 +2232,12 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
 	if (ring_buffer_flags != RB_BUFFERS_ON)
 		return NULL;
 
-	if (atomic_read(&buffer->record_disabled))
-		return NULL;
-
 	/* If we are tracing schedule, we don't want to recurse */
 	resched = ftrace_preempt_disable();
 
+	if (atomic_read(&buffer->record_disabled))
+		goto out_nocheck;
+
 	if (trace_recursive_lock())
 		goto out_nocheck;
 
@@ -2469,11 +2469,11 @@ int ring_buffer_write(struct ring_buffer *buffer,
 	if (ring_buffer_flags != RB_BUFFERS_ON)
 		return -EBUSY;
 
-	if (atomic_read(&buffer->record_disabled))
-		return -EBUSY;
-
 	resched = ftrace_preempt_disable();
 
+	if (atomic_read(&buffer->record_disabled))
+		goto out;
+
 	cpu = raw_smp_processor_id();
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Steven Rostedt]

On Mon, 2010-03-08 at 14:04 +0800, Li Zefan wrote:
> While running a ftrace test, a kernel warning showed up. The bug is not so
> easy to reproduce, normally it takes 30 mins to 2 hours.

What test are you running? Can you share it?

> 
> After revering 3c05d7482777f15e71bb4cb1ba78dee2800dfec6, I ran the test
> for 15 hours, and the bug seems disapeared.

So basically, you are reading both the trace and trace_pipe (or
trace_pipe_raw) at the same time?

-- Steve

> 
> ------------[ cut here ]------------
> WARNING: at kernel/trace/ring_buffer.c:3420 ring_buffer_reset_cpu+0x5a/0x9c()
> Hardware name: PRIMERGY                      
> Modules linked in: ipt_MASQUERADE iptable_nat nf_nat bridge stp llc deflate zlib_deflate ctr camellia cast5 rmd160 crypto_null ccm serpent blowfish twofish_x86_64 twofish_common ecb xcbc cbc sha256_generic sha512_generic des_generic cryptd aes_x86_64 aes_generic ah6 ah4 esp6 esp4 xfrm4_mode_beet xfrm4_tunnel tunnel4 xfrm4_mode_tunnel xfrm4_mode_transport xfrm6_mode_transport xfrm6_mode_beet ipcomp ipcomp6 xfrm_ipcomp xfrm6_tunnel tunnel6 af_key autofs4 sunrpc ipv6 dm_mirror dm_region_hash dm_log dm_multipath uinput i5k_amb hwmon e1000e i5000_edac edac_core iTCO_wdt iTCO_vendor_support shpchp i2c_i801 i2c_core serio_raw pcspkr pata_acpi ata_generic mptsas mptscsih ata_piix mptbase scsi_transport_sas dm_mod [last unloaded: speedstep_lib]
> Pid: 2108, comm: ftrace_current_ Tainted: G        W  2.6.33-tip+ #2
> Call Trace:
>  [<ffffffff8104ebd0>] warn_slowpath_common+0x7c/0x94
>  [<ffffffff8104ebfc>] warn_slowpath_null+0x14/0x16
>  [<ffffffff810a50f5>] ring_buffer_reset_cpu+0x5a/0x9c
>  [<ffffffff810aa3f0>] tracing_reset_online_cpus+0x4a/0x79
>  [<ffffffff810aa434>] tracer_init+0x15/0x20
>  [<ffffffff810aa601>] tracing_set_tracer+0x1c2/0x1e7
>  [<ffffffff810d9847>] ? might_fault+0x5c/0xac
>  [<ffffffff810aa6b2>] tracing_set_trace_write+0x8c/0xbc
>  [<ffffffff810a8e79>] ? trace_buffer_lock_reserve+0x21/0x56
>  [<ffffffff810a95ce>] ? trace_current_buffer_lock_reserve+0x16/0x18
>  [<ffffffff813ef135>] ? retint_swapgs+0x13/0x1b
>  [<ffffffff81104618>] vfs_write+0xae/0x10b
>  [<ffffffff81104735>] sys_write+0x4a/0x6e
>  [<ffffffff81009da6>] tracesys+0xd0/0xd5
> ---[ end trace f7002f0890d5b023 ]---

Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420

[Li Zefan]

Steven Rostedt wrote:
> On Mon, 2010-03-08 at 14:04 +0800, Li Zefan wrote:
>> While running a ftrace test, a kernel warning showed up. The bug is not so
>> easy to reproduce, normally it takes 30 mins to 2 hours.
> 
> What test are you running? Can you share it?
> 

The test runs 10+ processes, reading/writing files in debugfs/tracing/
simultaneously.

I'll send it to you in a private mail.

>> After revering 3c05d7482777f15e71bb4cb1ba78dee2800dfec6, I ran the test
>> for 15 hours, and the bug seems disapeared.
> 
> So basically, you are reading both the trace and trace_pipe (or
> trace_pipe_raw) at the same time?
> 

reading trace, yes. reading trace_pipe, no.

Actualy we don't see how this commit relates to the bug.
I'll run the test again to be sure on this.

> -- Steve
> 
>> ------------[ cut here ]------------
>> WARNING: at kernel/trace/ring_buffer.c:3420 ring_buffer_reset_cpu+0x5a/0x9c()
>> Hardware name: PRIMERGY                      
>> Modules linked in: ipt_MASQUERADE iptable_nat nf_nat bridge stp llc deflate zlib_deflate ctr camellia cast5 rmd160 crypto_null ccm serpent blowfish twofish_x86_64 twofish_common ecb xcbc cbc sha256_generic sha512_generic des_generic cryptd aes_x86_64 aes_generic ah6 ah4 esp6 esp4 xfrm4_mode_beet xfrm4_tunnel tunnel4 xfrm4_mode_tunnel xfrm4_mode_transport xfrm6_mode_transport xfrm6_mode_beet ipcomp ipcomp6 xfrm_ipcomp xfrm6_tunnel tunnel6 af_key autofs4 sunrpc ipv6 dm_mirror dm_region_hash dm_log dm_multipath uinput i5k_amb hwmon e1000e i5000_edac edac_core iTCO_wdt iTCO_vendor_support shpchp i2c_i801 i2c_core serio_raw pcspkr pata_acpi ata_generic mptsas mptscsih ata_piix mptbase scsi_transport_sas dm_mod [last unloaded: speedstep_lib]
>> Pid: 2108, comm: ftrace_current_ Tainted: G        W  2.6.33-tip+ #2
>> Call Trace:
>>  [<ffffffff8104ebd0>] warn_slowpath_common+0x7c/0x94
>>  [<ffffffff8104ebfc>] warn_slowpath_null+0x14/0x16
>>  [<ffffffff810a50f5>] ring_buffer_reset_cpu+0x5a/0x9c
>>  [<ffffffff810aa3f0>] tracing_reset_online_cpus+0x4a/0x79
>>  [<ffffffff810aa434>] tracer_init+0x15/0x20
>>  [<ffffffff810aa601>] tracing_set_tracer+0x1c2/0x1e7
>>  [<ffffffff810d9847>] ? might_fault+0x5c/0xac
>>  [<ffffffff810aa6b2>] tracing_set_trace_write+0x8c/0xbc
>>  [<ffffffff810a8e79>] ? trace_buffer_lock_reserve+0x21/0x56
>>  [<ffffffff810a95ce>] ? trace_current_buffer_lock_reserve+0x16/0x18
>>  [<ffffffff813ef135>] ? retint_swapgs+0x13/0x1b
>>  [<ffffffff81104618>] vfs_write+0xae/0x10b
>>  [<ffffffff81104735>] sys_write+0x4a/0x6e
>>  [<ffffffff81009da6>] tracesys+0xd0/0xd5
>> ---[ end trace f7002f0890d5b023 ]---
> 
> 
> 
>