From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <ak@linux.intel.com>
Cc: Song Liu <songliubraving@fb.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Kan Liang <kan.liang@linux.intel.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Josh Poimboeuf <jpoimboe@redhat.com>, Tejun Heo <tj@kernel.org>,
Andrii Nakryiko <andriin@fb.com>, Francis Ricci <fjricci@fb.com>
Subject: Re: WARNING with LBR + precise_ip=2 + bpf_get_stackid()
Date: Fri, 19 Jun 2020 10:13:36 +0200 [thread overview]
Message-ID: <20200619081336.GQ576905@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200618223555.GB793265@tassilo.jf.intel.com>
On Thu, Jun 18, 2020 at 03:35:55PM -0700, Andi Kleen wrote:
> > We noticed that this only happens with precise_ip >= 2. This is caused by
> > setup_pebs_fixed_sample_data() using pens->real_ip:
> >
> > set_linear_ip(regs, pebs->real_ip);
>
> With precise_ip == 1 the IP will be one instruction behind.
> That's the only difference to 2 or 3.
>
> So something about the actual instruction confuses the unwinder.
It's trying to do an unwind with the PEBS IP (or worse the whole PEBS
regset), which doesn't match the interrupt IP or the stack layout at
that time. Of course it doesn't work.
prev parent reply other threads:[~2020-06-19 8:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-18 17:25 WARNING with LBR + precise_ip=2 + bpf_get_stackid() Song Liu
2020-06-18 18:33 ` Peter Zijlstra
2020-06-18 20:18 ` Song Liu
2020-06-18 22:35 ` Andi Kleen
2020-06-18 23:21 ` Song Liu
2020-06-19 8:13 ` Peter Zijlstra [this message]
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