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From:   Song Liu <songliubraving@fb.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     linux-kernel <linux-kernel@vger.kernel.org>,
        Kan Liang <kan.liang@linux.intel.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
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        Francis Ricci <fjricci@fb.com>
Subject: Re: WARNING with LBR + precise_ip=2 + bpf_get_stackid()
Thread-Topic: WARNING with LBR + precise_ip=2 + bpf_get_stackid()
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Date:   Thu, 18 Jun 2020 20:18:06 +0000
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> On Jun 18, 2020, at 11:33 AM, Peter Zijlstra <peterz@infradead.org> wrote=
:
>=20
> On Thu, Jun 18, 2020 at 05:25:24PM +0000, Song Liu wrote:
>=20

[...]

>> 0xfffffe00004d1380 __start_orc_unwind
>> 0xfffffe00004d1388 unwind_next_frame.cold.7
>> 0xfffffe00004d13c8 perf_callchain_kernel
>> 0xfffffe00004d1418 entry_SYSCALL_64
>> 0xfffffe00004d1450 get_perf_callchain
>> 0xfffffe00004d14b0 bpf_get_stack
>=20
> This, this is where it gets buggerd. This is a BPF problem, not a perf
> problem.
>=20
> You'll note that if you ask perf for a PERF_SAMPLE_CALLCHAIN we'll do
> that early in setup_pebs_fixed_sample_data().

We did notice perf works fine in similar scenario. I guess need similar=20
logic in BPF.=20

Thanks,
Song