linux-kernel - Re: WARNING with LBR + precise_ip=2 + bpf_get

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Date:   Thu, 18 Jun 2020 20:18:06 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     linux-kernel <linux-kernel@...r.kernel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>, Tejun Heo <tj@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Francis Ricci <fjricci@...com>
Subject: Re: WARNING with LBR + precise_ip=2 + bpf_get_stackid()



> On Jun 18, 2020, at 11:33 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Thu, Jun 18, 2020 at 05:25:24PM +0000, Song Liu wrote:
> 

[...]

>> 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
> 
> This, this is where it gets buggerd. This is a BPF problem, not a perf
> problem.
> 
> 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 
logic in BPF. 

Thanks,
Song