linux-kernel - Re: [PATCH] bpf: fix sample_flags for bpf_perf_event

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Date:   Mon, 17 Oct 2022 23:35:44 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     SeongJae Park <sj@...nel.org>,
        Sumanth Korikkar <sumanthk@...ux.ibm.com>, olsajiri@...il.com,
        bpf@...r.kernel.org, gor@...ux.ibm.com, hca@...ux.ibm.com,
        iii@...ux.ibm.com, linux-kernel@...r.kernel.org,
        linux-tip-commits@...r.kernel.org, peterz@...radead.org,
        svens@...ux.ibm.com, tip-bot2@...utronix.de, tmricht@...ux.ibm.com,
        x86@...nel.org
Subject: Re: [PATCH] bpf: fix sample_flags for bpf_perf_event_output

On Mon, 17 Oct 2022 15:52:15 -0700 Namhyung Kim <namhyung@...nel.org> wrote:

> Hi SeongJae,
> 
> On Mon, Oct 17, 2022 at 12:27 PM SeongJae Park <sj@...nel.org> wrote:
> >
> > Hello,
> >
> >
> > The commit that this patch is fixing[1] also causes yet another segfault for
> > 'perf-script' of tracepoint records.  For example:
> >
> >     $ sudo timeout 3 perf record -e exceptions:page_fault_user
> >     [ perf record: Woken up 1 times to write data ]
> >     [ perf record: Captured and wrote 0.228 MB perf.data (74 samples) ]
> >     $ sudo perf script
> >     Segmentation fault
> >
> > Reverting this patch and the original bug commit[1] fixes the issue.  I haven't
> > deep dive yet because I'm not familiar with this area.  Anybody has any idea
> > about this?
> >
> > [1] 838d9bb62d13 ("perf: Use sample_flags for raw_data")
> 
> Sorry for the trouble.

No problem.

> I think you also need to apply the below:
> 
> https://lore.kernel.org/r/20221012143857.48198-1-james.clark@arm.com

Thank you for this nice answer.  I confirmed that this fixes my issue.


Thanks,
SJ

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