Re: [PATCH] tools lib traceevent: add checks for returned EVENT_ERROR type

[Dean Nelson]

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@aarch64 ~]# 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@aarch64 ~]#
>
> 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@krava 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@xxxxxxxxxx>
> > ---
> >   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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