From: Aleksa Sarai <cyphar@cyphar.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S. Miller" <davem@davemloft.net>,
Masami Hiramatsu <mhiramat@kernel.org>,
Jonathan Corbet <corbet@lwn.net>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Shuah Khan <shuah@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Brendan Gregg <bgregg@netflix.com>,
Christian Brauner <christian@brauner.io>,
Aleksa Sarai <asarai@suse.de>,
netdev@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v3 1/2] kretprobe: produce sane stack traces
Date: Sun, 4 Nov 2018 22:59:13 +1100 [thread overview]
Message-ID: <20181104115913.74l4yzecisvtt2j5@yavin> (raw)
In-Reply-To: <20181103070253.ajrqzs5xu2vf5stu@yavin>
[-- Attachment #1: Type: text/plain, Size: 1619 bytes --]
On 2018-11-03, Aleksa Sarai <cyphar@cyphar.com> wrote:
> This is actually a general bug in ftrace as well, because (for
> instance) while the unwinder calls into ftrace_graph_ret_addr() while
> walking up the stack this isn't used to correct regs->ip in
> perf_callchain_kernel(). I think this is the cause of the bug in
> ftrace-graph (if you switch to the "frame" unwinder you might be able
> to see it more clearly) -- but when trying to fix it I'm having
> trouble figuring out what retp should be (stack_addr(regs) doesn't
> give the right result for some reason).
@Steven, @Masami: Can you verify whether this is an actual bug? The
snippet is like (arch/x86/events/core.c):
void
perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
{
/* ... */
if (perf_callchain_store(entry, regs->ip))
return;
/* rest of unwind code */
}
And it seems to me that there's an ftrace_graph_ret_addr missing here
(though I was having trouble figuring out what the right retp would be
in this context -- both stack_addr(regs) and ®s->sp appear to be
wrong when I was trying to get this to work with kretprobes -- while my
patch worked with all other kretprobe_trampoline cases in the unwinder).
The same issue is present in __save_stack_trace
(arch/x86/kernel/stacktrace.c). This is likely the only reason that --
as Steven said -- stacktraces wouldn't work with ftrace-graph (and thus
with the refactor both of you are discussing).
Thanks.
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2018-11-04 11:59 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 8:35 [PATCH v3 0/2] kretprobe: produce sane stack traces Aleksa Sarai
2018-11-01 8:35 ` [PATCH v3 1/2] " Aleksa Sarai
2018-11-01 15:20 ` Masami Hiramatsu
2018-11-01 21:13 ` Aleksa Sarai
2018-11-02 3:04 ` Masami Hiramatsu
2018-11-02 4:37 ` Aleksa Sarai
2018-11-03 12:47 ` Masami Hiramatsu
2018-11-02 0:47 ` Steven Rostedt
2018-11-02 5:05 ` Aleksa Sarai
2018-11-02 6:59 ` Aleksa Sarai
2018-11-02 13:16 ` Steven Rostedt
2018-11-02 15:43 ` Josh Poimboeuf
2018-11-02 16:13 ` Steven Rostedt
2018-11-03 13:00 ` Masami Hiramatsu
2018-11-03 13:13 ` Steven Rostedt
2018-11-03 16:34 ` Masami Hiramatsu
2018-11-03 17:30 ` Steven Rostedt
2018-11-03 17:33 ` Steven Rostedt
2018-11-04 2:25 ` Masami Hiramatsu
2018-11-03 7:02 ` Aleksa Sarai
2018-11-04 11:59 ` Aleksa Sarai [this message]
2018-11-06 22:15 ` Steven Rostedt
2018-11-08 7:46 ` Aleksa Sarai
2018-11-08 8:04 ` Aleksa Sarai
2018-11-08 14:44 ` Josh Poimboeuf
2018-11-09 7:26 ` Masami Hiramatsu
2018-11-09 15:10 ` Aleksa Sarai
2018-11-09 7:15 ` Masami Hiramatsu
2018-11-09 15:06 ` Aleksa Sarai
2018-11-10 15:31 ` Masami Hiramatsu
2018-11-12 10:38 ` Aleksa Sarai
2018-11-03 13:23 ` Masami Hiramatsu
2018-11-02 7:58 ` Aleksa Sarai
2018-11-02 4:01 ` kbuild test robot
2018-11-01 8:35 ` [PATCH v3 2/2] trace: remove kretprobed checks Aleksa Sarai
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