[PATCH 1/2] arm64: stacktrace: avoid listing stacktrace functions in stacktrace

[PATCH 1/2] arm64: stacktrace: avoid listing stacktrace functions in stacktrace

[Prakash Gupta]

The stacktraces always begin as follows:

 [<c00117b4>] save_stack_trace_tsk+0x0/0x98
 [<c0011870>] save_stack_trace+0x24/0x28
 ...

This is because the stack trace code includes the stack frames for itself.
This is incorrect behaviour, and also leads to "skip" doing the wrong thing
(which is the number of stack frames to avoid recording.)

Perversely, it does the right thing when passed a non-current thread.  Fix
this by ensuring that we have a known constant number of frames above the
main stack trace function, and always skip these.

This was fixed for arch arm by Commit 3683f44c42e9 ("ARM: stacktrace: avoid
listing stacktrace functions in stacktrace")

Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
---
 arch/arm64/kernel/stacktrace.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 3144584617e7..76809ccd309c 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -140,7 +140,8 @@ void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;
 }
 
-void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+static noinline void __save_stack_trace(struct task_struct *tsk,
+	struct stack_trace *trace, unsigned int nosched)
 {
 	struct stack_trace_data data;
 	struct stackframe frame;
@@ -150,15 +151,16 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 
 	data.trace = trace;
 	data.skip = trace->skip;
+	data.no_sched_functions = nosched;
 
 	if (tsk != current) {
-		data.no_sched_functions = 1;
 		frame.fp = thread_saved_fp(tsk);
 		frame.pc = thread_saved_pc(tsk);
 	} else {
-		data.no_sched_functions = 0;
+		/* We don't want this function nor the caller */
+		data.skip += 2;
 		frame.fp = (unsigned long)__builtin_frame_address(0);
-		frame.pc = (unsigned long)save_stack_trace_tsk;
+		frame.pc = (unsigned long)__save_stack_trace;
 	}
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	frame.graph = tsk->curr_ret_stack;
@@ -172,9 +174,15 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
+	__save_stack_trace(tsk, trace, 1);
+}
+
 void save_stack_trace(struct stack_trace *trace)
 {
-	save_stack_trace_tsk(current, trace);
+	__save_stack_trace(current, trace, 0);
 }
+
 EXPORT_SYMBOL_GPL(save_stack_trace);
 #endif
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[PATCH 2/2] mm, page_owner: Skip unnecessary stack_trace entries

[Prakash Gupta]

The page_owner stacktrace always begin as follows:

[<ffffff987bfd48f4>] save_stack+0x40/0xc8
[<ffffff987bfd4da8>] __set_page_owner+0x3c/0x6c

These two entries do not provide any useful information and limits the
available stacktrace depth.  The page_owner stacktrace was skipping caller
function from stack entries but this was missed with commit f2ca0b557107
("mm/page_owner: use stackdepot to store stacktrace")

Example page_owner entry after the patch:

Page allocated via order 0, mask 0x8(ffffff80085fb714)
PFN 654411 type Movable Block 639 type CMA Flags 0x0(ffffffbe5c7f12c0)
[<ffffff9b64989c14>] post_alloc_hook+0x70/0x80
...
[<ffffff9b651216e8>] msm_comm_try_state+0x5f8/0x14f4
[<ffffff9b6512486c>] msm_vidc_open+0x5e4/0x7d0
[<ffffff9b65113674>] msm_v4l2_open+0xa8/0x224

Fixes: f2ca0b557107 ("mm/page_owner: use stackdepot to store stacktrace")
Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
---
 mm/page_owner.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 10d16fc45bd9..75b7c39bf1df 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -139,7 +139,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
 		.nr_entries = 0,
 		.entries = entries,
 		.max_entries = PAGE_OWNER_STACK_DEPTH,
-		.skip = 0
+		.skip = 2
 	};
 	depot_stack_handle_t handle;
 
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Re: [PATCH 2/2] mm, page_owner: Skip unnecessary stack_trace entries

[Vlastimil Babka]

On 08/30/2017 09:32 AM, Prakash Gupta wrote:
> The page_owner stacktrace always begin as follows:
> 
> [<ffffff987bfd48f4>] save_stack+0x40/0xc8
> [<ffffff987bfd4da8>] __set_page_owner+0x3c/0x6c

Hmm, on x86_64 it looks like this:

 save_stack_trace+0x16/0x20
 save_stack+0x43/0xe0
 __set_page_owner+0x24/0x50

So after your patch there's still __set_page_owner. Seems x86 needs
something similar to your arm64 patch 1/2?

> These two entries do not provide any useful information and limits the
> available stacktrace depth.  The page_owner stacktrace was skipping caller
> function from stack entries but this was missed with commit f2ca0b557107
> ("mm/page_owner: use stackdepot to store stacktrace")
> 
> Example page_owner entry after the patch:
> 
> Page allocated via order 0, mask 0x8(ffffff80085fb714)
> PFN 654411 type Movable Block 639 type CMA Flags 0x0(ffffffbe5c7f12c0)
> [<ffffff9b64989c14>] post_alloc_hook+0x70/0x80
> ...
> [<ffffff9b651216e8>] msm_comm_try_state+0x5f8/0x14f4
> [<ffffff9b6512486c>] msm_vidc_open+0x5e4/0x7d0
> [<ffffff9b65113674>] msm_v4l2_open+0xa8/0x224
> 
> Fixes: f2ca0b557107 ("mm/page_owner: use stackdepot to store stacktrace")
> Signed-off-by: Prakash Gupta <guptap@codeaurora.org>

The patch itself improves the output regardless of whether we fix the
x86 internals, so:

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/page_owner.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 10d16fc45bd9..75b7c39bf1df 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -139,7 +139,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
>  		.nr_entries = 0,
>  		.entries = entries,
>  		.max_entries = PAGE_OWNER_STACK_DEPTH,
> -		.skip = 0
> +		.skip = 2
>  	};
>  	depot_stack_handle_t handle;
>  
> 

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Re: [PATCH 2/2] mm, page_owner: Skip unnecessary stack_trace entries

[Prakash Gupta]

On 8/31/2017 1:04 PM, Vlastimil Babka wrote:
> On 08/30/2017 09:32 AM, Prakash Gupta wrote:
>> The page_owner stacktrace always begin as follows:
>>
>> [<ffffff987bfd48f4>] save_stack+0x40/0xc8
>> [<ffffff987bfd4da8>] __set_page_owner+0x3c/0x6c
> 
> Hmm, on x86_64 it looks like this:
> 
>   save_stack_trace+0x16/0x20
>   save_stack+0x43/0xe0
>   __set_page_owner+0x24/0x50
> 
> So after your patch there's still __set_page_owner. Seems x86 needs
> something similar to your arm64 patch 1/2?

Yes, that's correct.

> 
>> These two entries do not provide any useful information and limits the
>> available stacktrace depth.  The page_owner stacktrace was skipping caller
>> function from stack entries but this was missed with commit f2ca0b557107
>> ("mm/page_owner: use stackdepot to store stacktrace")
>>
>> Example page_owner entry after the patch:
>>
>> Page allocated via order 0, mask 0x8(ffffff80085fb714)
>> PFN 654411 type Movable Block 639 type CMA Flags 0x0(ffffffbe5c7f12c0)
>> [<ffffff9b64989c14>] post_alloc_hook+0x70/0x80
>> ...
>> [<ffffff9b651216e8>] msm_comm_try_state+0x5f8/0x14f4
>> [<ffffff9b6512486c>] msm_vidc_open+0x5e4/0x7d0
>> [<ffffff9b65113674>] msm_v4l2_open+0xa8/0x224
>>
>> Fixes: f2ca0b557107 ("mm/page_owner: use stackdepot to store stacktrace")
>> Signed-off-by: Prakash Gupta <guptap@codeaurora.org>
> 
> The patch itself improves the output regardless of whether we fix the
> x86 internals, so:
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks.

> 
>> ---
>>   mm/page_owner.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/page_owner.c b/mm/page_owner.c
>> index 10d16fc45bd9..75b7c39bf1df 100644
>> --- a/mm/page_owner.c
>> +++ b/mm/page_owner.c
>> @@ -139,7 +139,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
>>   		.nr_entries = 0,
>>   		.entries = entries,
>>   		.max_entries = PAGE_OWNER_STACK_DEPTH,
>> -		.skip = 0
>> +		.skip = 2
>>   	};
>>   	depot_stack_handle_t handle;
>>   
>>
> 

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Re: [PATCH 1/2] arm64: stacktrace: avoid listing stacktrace functions in stacktrace

[Andrew Morton]

On Wed, 30 Aug 2017 13:02:22 +0530 Prakash Gupta <guptap@codeaurora.org> wrote:

> The stacktraces always begin as follows:
> 
>  [<c00117b4>] save_stack_trace_tsk+0x0/0x98
>  [<c0011870>] save_stack_trace+0x24/0x28
>  ...
> 
> This is because the stack trace code includes the stack frames for itself.
> This is incorrect behaviour, and also leads to "skip" doing the wrong thing
> (which is the number of stack frames to avoid recording.)
> 
> Perversely, it does the right thing when passed a non-current thread.  Fix
> this by ensuring that we have a known constant number of frames above the
> main stack trace function, and always skip these.
> 
> This was fixed for arch arm by Commit 3683f44c42e9 ("ARM: stacktrace: avoid
> listing stacktrace functions in stacktrace")

I can take this (with acks, please?)

3683f44c42e9 has a cc:stable but your patch does not.  Should it?

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Re: [PATCH 1/2] arm64: stacktrace: avoid listing stacktrace functions in stacktrace

[Prakash Gupta]

On 8/31/2017 1:58 AM, Andrew Morton wrote:
> On Wed, 30 Aug 2017 13:02:22 +0530 Prakash Gupta <guptap@codeaurora.org> wrote:
> 
>> The stacktraces always begin as follows:
>>
>>   [<c00117b4>] save_stack_trace_tsk+0x0/0x98
>>   [<c0011870>] save_stack_trace+0x24/0x28
>>   ...
>>
>> This is because the stack trace code includes the stack frames for itself.
>> This is incorrect behaviour, and also leads to "skip" doing the wrong thing
>> (which is the number of stack frames to avoid recording.)
>>
>> Perversely, it does the right thing when passed a non-current thread.  Fix
>> this by ensuring that we have a known constant number of frames above the
>> main stack trace function, and always skip these.
>>
>> This was fixed for arch arm by Commit 3683f44c42e9 ("ARM: stacktrace: avoid
>> listing stacktrace functions in stacktrace")
> 
> I can take this (with acks, please?)
> 
> 3683f44c42e9 has a cc:stable but your patch does not.  Should it?
> 

My bad, it should be copied to stable as well.

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Re: [PATCH 1/2] arm64: stacktrace: avoid listing stacktrace functions in stacktrace

[Catalin Marinas]

On Wed, Aug 30, 2017 at 01:28:28PM -0700, Andrew Morton wrote:
> On Wed, 30 Aug 2017 13:02:22 +0530 Prakash Gupta <guptap@codeaurora.org> wrote:
> 
> > The stacktraces always begin as follows:
> > 
> >  [<c00117b4>] save_stack_trace_tsk+0x0/0x98
> >  [<c0011870>] save_stack_trace+0x24/0x28
> >  ...
> > 
> > This is because the stack trace code includes the stack frames for itself.
> > This is incorrect behaviour, and also leads to "skip" doing the wrong thing
> > (which is the number of stack frames to avoid recording.)
> > 
> > Perversely, it does the right thing when passed a non-current thread.  Fix
> > this by ensuring that we have a known constant number of frames above the
> > main stack trace function, and always skip these.
> > 
> > This was fixed for arch arm by Commit 3683f44c42e9 ("ARM: stacktrace: avoid
> > listing stacktrace functions in stacktrace")
> 
> I can take this (with acks, please?)

In case you haven't picked it up already:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

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