From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Andrey Konovalov <andreyknvl@google.com>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH tip/master v4] kprobes: extable: Identify kprobes' insn-slots as kernel text area
Date: Mon, 9 Jan 2017 11:36:48 -0600 [thread overview]
Message-ID: <20170109173648.k7dxu7nz22qc6upq@treble> (raw)
In-Reply-To: <148388747896.6869.6354262871751682264.stgit@devbox>
On Sun, Jan 08, 2017 at 11:58:09PM +0900, Masami Hiramatsu wrote:
> Make __kernel_text_address()/kernel_text_address() returns
> true if the given address is on a kprobe's instruction slot,
> which is generated by kprobes as a trampoline code.
> This can help stacktraces to determine the address is on a
> text area or not.
>
> To implement this without any sleep in is_kprobe_*_slot(),
> this also modify insn_cache page list as a rcu list. It may
> increase processing deley (not processing time) for garbage
> slot collection, because it requires to wait an additional
> rcu grance period when freeing a page from the list.
> However, since it is not a hot path, we may not take care of it.
>
> Note: this can give a small overhead to stack unwinders because
> this adds 2 checks in __kernel_text_address(). However, the
> impact should be very small, kprobe_insn_pages list has 1 entry
> per 256 probes(on x86, on arm/arm64 it will be 1024 probes),
> and kprobe_optinsn_pages has 1 entry per 32 probes(on x86).
> In most use cases, the number of kprobe events may be less
> than 20, this means is_kprobe_*_slot() will check just 1 entry.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Thanks for doing this Masami! I verified that it works:
Tested-by: Josh Poimboeuf <jpoimboe@redhat.com>
I suspect that BPF generated code also has the same issue, so I'll leave
the unwinder warning disabled for now.
BTW, I think we'll have more problems with generated code if/when we
move to an x86 DWARF unwinder, because it won't have any idea how to
unwind past generated code. Long term I wonder if it would make sense
to create some kind of framework for creating or registering generated
code, so we can solve these types of problems in a single place.
--
Josh
next prev parent reply other threads:[~2017-01-09 17:36 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-22 6:42 Detecting kprobes generated code addresses Josh Poimboeuf
2016-12-25 3:13 ` Masami Hiramatsu
2016-12-25 6:16 ` Masami Hiramatsu
2016-12-26 4:30 ` Masami Hiramatsu
2016-12-26 14:50 ` [PATCH tip/master] kprobes: extable: Identify kprobes' insn-slots as kernel text area Masami Hiramatsu
2016-12-26 15:34 ` [PATCH tip/master v2] " Masami Hiramatsu
2016-12-26 17:21 ` kbuild test robot
2016-12-26 17:46 ` kbuild test robot
2016-12-27 6:13 ` Masami Hiramatsu
2016-12-27 6:14 ` [PATCH tip/master v3] " Masami Hiramatsu
2017-01-03 10:54 ` Peter Zijlstra
2017-01-04 5:06 ` Masami Hiramatsu
2017-01-04 10:01 ` Peter Zijlstra
2017-01-08 4:22 ` Masami Hiramatsu
2017-01-08 12:31 ` Masami Hiramatsu
2017-01-08 14:58 ` [PATCH tip/master v4] " Masami Hiramatsu
2017-01-09 17:36 ` Josh Poimboeuf [this message]
2017-01-10 1:11 ` Masami Hiramatsu
2017-01-10 8:59 ` Peter Zijlstra
2017-01-10 21:42 ` Josh Poimboeuf
2017-01-11 9:57 ` Masami Hiramatsu
2017-01-14 9:56 ` [tip:perf/core] kprobes, extable: Identify kprobes trampolines " tip-bot for Masami Hiramatsu
2017-01-04 14:21 ` [PATCH tip/master v3] kprobes: extable: Identify kprobes' insn-slots " Steven Rostedt
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