linux-kernel - Re: [PATCH] tools lib traceevent: add checks for returned EVENT

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Date:	Fri, 7 Aug 2015 08:01:02 -0500
From:	Dean Nelson <dnelson@...hat.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	a.p.zijlstra@...llo.org, mingo@...hat.com, rostedt@...dmis.org,
	acme@...nel.org, linux-kernel@...r.kernel.org, jolsa@...nel.org,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] tools lib traceevent: add checks for returned EVENT_ERROR
 type

On 08/07/2015 05:59 AM, Jiri Olsa wrote:
> On Mon, Aug 03, 2015 at 01:08:05PM -0400, Dean Nelson wrote:
>> Running the following perf-stat command on an arm64 system produces the
>> following result...
>>
>>    [root@...ch64 ~]# perf stat -e kmem:mm_page_alloc -a sleep 1
>>      Warning: [kmem:mm_page_alloc] function sizeof not defined
>>      Warning: Error: expected type 4 but read 0
>>    Segmentation fault
>>    [root@...ch64 ~]#
>
> hum, what kernel are you running on? I dont see that warning

The system is based on v4.2-rc3 and my .config has...

   CONFIG_SPARSEMEM_VMEMMAP=y

which matters, as the sizeof operator is introduced through...

   #define pfn_to_page __pfn_to_page

when __pfn_to_page is defined as...

   #define __pfn_to_page(pfn)      (vmemmap + (pfn))

which only happens when '#elif defined(CONFIG_SPARSEMEM_VMEMMAP)' is
true.

Now vmemmap was redefined about a year ago by commit 08375198b01001c0e43b
to be...

   #define VMEMMAP_SIZE            ALIGN((1UL << (VA_BITS - PAGE_SHIFT)) 
* sizeof(struct page), PUD_SIZE)
   #define VMALLOC_END             (PAGE_OFFSET - PUD_SIZE - 
VMEMMAP_SIZE - SZ_64K)
   #define vmemmap                 ((struct page *)(VMALLOC_END + SZ_64K))

And VMEMMAP_SIZE has the sizeof operator. The ALIGN() macro introduces
a typeof operator which also would be an issue if the parser had gotten
that far.

This vmemmap stuff can be found in arch/arm64/include/asm/pgtable.h.

Now backing up a step or two, the pfn_to_page() macro is referenced in
include/trace/events/kmem.h as the first of the 'args' passed to
TP_prink()...

   TRACE_EVENT(mm_page_alloc,
           :
           TP_printk("page=%p pfn=%lu order=%d migratetype=%d gfp_flags=%s",
                   __entry->pfn != -1UL ? pfn_to_page(__entry->pfn) : NULL,
                   __entry->pfn != -1UL ? __entry->pfn : 0,
                   __entry->order,
                   __entry->migratetype,
                   show_gfp_flags(__entry->gfp_flags))
   );

Hope that helps.


> on my system:
>
> [jolsa@...va perf]$ sudo ./perf stat -e kmem:mm_page_alloc -a sleep 1
>
>   Performance counter stats for 'system wide':
>
>                 227      kmem:mm_page_alloc
>
>         1.000762466 seconds time elapsed
>
> Cc-ing Namhyung
>
>
> jirka
>
>>
>> The second warning message and SIGSEGV stem from the issue expressed in the
>> first warning message, and are the result of ignoring the EVENT_ERROR type
>> returned back through the call chain.
>>
>> Dealing with the first warning message is beyond the scope of this patch. But
>> the second warning is addressed by this patch's first hunk. And the SIGSEGV is
>> eliminated by its second hunk.
>>
>> Signed-off-by: Dean Nelson <dnelson@...hat.com>
>> ---
>>   tools/lib/traceevent/event-parse.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
>> index cc25f05..72e2933 100644
>> --- a/tools/lib/traceevent/event-parse.c
>> +++ b/tools/lib/traceevent/event-parse.c
>> @@ -1680,6 +1680,9 @@ process_cond(struct event_format *event, struct print_arg *top, char **tok)
>>   	type = process_arg(event, left, &token);
>>
>>    again:
>> +	if (type == EVENT_ERROR)
>> +		goto out_free;
>> +
>>   	/* Handle other operations in the arguments */
>>   	if (type == EVENT_OP && strcmp(token, ":") != 0) {
>>   		type = process_op(event, left, &token);
>> @@ -1940,7 +1943,7 @@ process_op(struct event_format *event, struct print_arg *arg, char **tok)
>>
>>   		type = process_arg_token(event, right, tok, type);
>>
>> -		if (right->type == PRINT_OP &&
>> +		if (type != EVENT_ERROR && right->type == PRINT_OP &&
>>   		    get_op_prio(arg->op.op) < get_op_prio(right->op.op)) {
>>   			struct print_arg tmp;
>>
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