linux-kernel - perf segfault in in ordered_events_

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Date:   Wed, 16 Jan 2019 10:57:49 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     open list <linux-kernel@...r.kernel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     acme@...nel.org
Subject: perf segfault in in ordered_events__free()

Hi,

We are debugging a segfault of perf in ordered_events__free().
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;

Does this theory make sense? If so, what would be the best fix?

Thanks in advance!
Song