From: Peter Zijlstra <peterz@infradead.org>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Josh Poimboeuf <jpoimboe@kernel.org>, Song Liu <song@kernel.org>,
bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
x86@kernel.org, Yonghong Song <yhs@fb.com>,
Song Liu <songliubraving@fb.com>,
Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCHv2 1/4] Revert "perf/x86: Always store regs->ip in perf_callchain_kernel()"
Date: Thu, 6 Nov 2025 13:27:11 +0100 [thread overview]
Message-ID: <20251106122711.GV4067720@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20251103220924.36371-2-jolsa@kernel.org>
On Mon, Nov 03, 2025 at 11:09:21PM +0100, Jiri Olsa wrote:
> This reverts commit 83f44ae0f8afcc9da659799db8693f74847e66b3.
>
> Currently we store initial stacktrace entry twice for non-HW ot_regs, which
> means callers that fail perf_hw_regs(regs) condition in perf_callchain_kernel.
>
> It's easy to reproduce this bpftrace:
>
> # bpftrace -e 'tracepoint:sched:sched_process_exec { print(kstack()); }'
> Attaching 1 probe...
>
> bprm_execve+1767
> bprm_execve+1767
> do_execveat_common.isra.0+425
> __x64_sys_execve+56
> do_syscall_64+133
> entry_SYSCALL_64_after_hwframe+118
>
> When perf_callchain_kernel calls unwind_start with first_frame, AFAICS
> we do not skip regs->ip, but it's added as part of the unwind process.
> Hence reverting the extra perf_callchain_store for non-hw regs leg.
>
> I was not able to bisect this, so I'm not really sure why this was needed
> in v5.2 and why it's not working anymore, but I could see double entries
> as far as v5.10.
Probably some ftrace/bpf glue code that doesn't adhere to the contract
set by perf_hw_regs(); as you find in the next patch.
next prev parent reply other threads:[~2025-11-06 12:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-03 22:09 [PATCHv2 0/4] x86/fgraph,bpf: Fix ORC stack unwind from return probe Jiri Olsa
2025-11-03 22:09 ` [PATCHv2 1/4] Revert "perf/x86: Always store regs->ip in perf_callchain_kernel()" Jiri Olsa
2025-11-06 12:27 ` Peter Zijlstra [this message]
2025-11-03 22:09 ` [PATCHv2 2/4] x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe Jiri Olsa
2025-11-03 23:47 ` bot+bpf-ci
2025-11-04 9:27 ` Jiri Olsa
2025-11-06 12:29 ` Peter Zijlstra
2025-11-07 22:22 ` Alexei Starovoitov
2025-11-03 22:09 ` [PATCHv2 3/4] selftests/bpf: Add stacktrace ips test for kprobe_multi/kretprobe_multi Jiri Olsa
2025-11-03 22:09 ` [PATCHv2 4/4] selftests/bpf: Add stacktrace ips test for raw_tp Jiri Olsa
2025-11-03 23:47 ` bot+bpf-ci
2025-11-04 8:35 ` Jiri Olsa
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