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Date:   Wed, 16 Jan 2019 22:34:25 +0100
From:   Jiri Olsa <jolsa@redhat.com>
To:     Song Liu <liu.song.a23@gmail.com>
Cc:     open list <linux-kernel@vger.kernel.org>,
        Jiri Olsa <jolsa@kernel.org>, acme@kernel.org
Subject: Re: perf segfault in in ordered_events__free()
Message-ID: <20190116213425.GA16366@krava>
References: <CAPhsuW4EiGUo=p=KYsu+kGWVFRoxEjF3Bq_32QvakQjCsAAjFQ@mail.gmail.com>
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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) {