linux-kernel - Re: [lkp-robot] [x86/mm/ptdump] 243b72aae2: WARNING:at_arch/x86/mm/dump_pagetables.c:#note

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Date:   Tue, 28 Feb 2017 01:11:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     kernel test robot <xiaolong.ye@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Tobias Regnery <tobias.regnery@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>, <lkp@...org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [lkp-robot] [x86/mm/ptdump] 243b72aae2:
 WARNING:at_arch/x86/mm/dump_pagetables.c:#note_page

On Mon, 27 Feb 2017 16:01:34 +0300
Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:

> On 02/27/2017 04:03 AM, kernel test robot wrote:
> > 
> > FYI, we noticed the following commit:
> > 
> > commit: 243b72aae28ca1032284028323bb81c9235b15c9 ("x86/mm/ptdump: Optimize check for W+X mappings for CONFIG_KASAN=y")
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> ...
> > 
> > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> > 
> > 
> > +-----------------------------------------------------+------------+------------+
> > |                                                     | 5b1ad68f9b | 243b72aae2 |
> > +-----------------------------------------------------+------------+------------+
> > | boot_successes                                      | 0          | 0          |
> > | boot_failures                                       | 8          | 6          |
> > | BUG:KASAN:slab-out-of-bounds                        | 8          | 6          |
> > | WARNING:at_arch/x86/mm/dump_pagetables.c:#note_page | 0          | 6          |
> > +-----------------------------------------------------+------------+------------+
> 
> Ok, I reproduced this, but it's definitely caused *not* by 243b72aae28.
> This WARN is also reproducible on the parent commit 5b1ad68f9b.
> The only difference here is that on parent one needs dozens of seconds to reach this WARNING.
> It seems that this time difference somehow confused the robot.
> 
> As for the warning itself, it caused by kprobes. krpobe code use module_alloc() which
> creates these RWX mappings.
> I'm not sure how to fix this as AFAIK kprobes actually need RWX mapping.

Thanks! I also noticed this issue. I actually have a plan to make kprobes with R+X mappings (as ftrace does).
I'll queue this on my TODO list.



-- 
Masami Hiramatsu <mhiramat@...nel.org>