Re: perf segfault in in ordered_events__free()

[Jiri Olsa]

On Wed, Jan 16, 2019 at 10:57:49AM -0800, Song Liu wrote:
> Hi,
> 
> We are debugging a segfault of perf in ordered_events__free().

hi,
any backtrace or info on how to reproduce it?

> Disassemble shows the segfault was caused by oe->buff == NULL
> in the following line:
> 
>         /*
>          * Current buffer might not have all the events allocated
>          * yet, we need to free only allocated ones ...
>          */
>         list_del(&oe->buffer->list);
> 
> After poking around the code, I suspect it is caused by the following
> condition in alloc_event():
> 
>         } else if (oe->buffer) {
>                 new = &oe->buffer->event[oe->buffer_idx];
>                 if (++oe->buffer_idx == MAX_SAMPLE_BUFFER)
>                         oe->buffer = NULL;


argh.. yea, we need to check oe->buffer in ordered_events__free

would attached change fix it for you?

thanks,
jirka


---
diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
index 897589507d97..ea523d3b248f 100644
--- a/tools/perf/util/ordered-events.c
+++ b/tools/perf/util/ordered-events.c
@@ -391,8 +391,10 @@ void ordered_events__free(struct ordered_events *oe)
         * Current buffer might not have all the events allocated
         * yet, we need to free only allocated ones ...
         */
-       list_del(&oe->buffer->list);
-       ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
+       if (oe->buffer) {
+               list_del(&oe->buffer->list);
+               ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
+       }
 
        /* ... and continue with the rest */
        list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {