From: Jiri Slaby <jslaby@suse.cz>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Hurley <peter@hurleysoftware.com>,
Greg KH <gregkh@linuxfoundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
stable <stable@vger.kernel.org>,
lwn@lwn.net, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: BUG: unable to handle kernel paging request from pty_write [was: Linux 4.4.2]
Date: Fri, 26 Feb 2016 09:56:17 +0100 [thread overview]
Message-ID: <56D01331.5030401@suse.cz> (raw)
In-Reply-To: <CA+55aFzQzCKhX73bUYwNMK8Dd9ECtmav8u7ds2aXKjEo7DV3Gg@mail.gmail.com>
On 02/26/2016, 01:38 AM, Linus Torvalds wrote:
> On Thu, Feb 25, 2016 at 1:32 PM, Jiri Slaby <jslaby@suse.cz> wrote:
>>
>> Interestingly, RBP contains address inside try_to_wake_up --
>> ffffffff810a535a (dunno why) which is:
>> ffffffff810a5355: e8 66 a0 ff ff callq ffffffff8109f3c0
>> <ttwu_stat>
>> ffffffff810a535a: e9 9d fe ff ff jmpq ffffffff810a51fc
>> <try_to_wake_up+0x3c>
>>
>> ttwu_stat does in the begginning:
>> mov $0x16e80,%r14
>>
>> which is what we actually still have in r14 when it crashes. The first
>> ttwu_stat's "if" has to go through the true branch (otherwise r14 would
>> be overwritten).
>
> Hmm. That does sound very much like it might be ttwu_stat() that has
> gotten the stack frame wrong, and when finishes exits, it does
>
> popq %rbp
> ret
>
> but in fact it popped the return address, and then returned to a crazy address.
>
> Which sounds like a corrupted stack pointer (not a corrupted stack).
>
> Can you make just the "vmlinux" file available somewhere?
Sure, both vmlinux w/ its separated .debuginfo sections vmlinux.debug
are at:
http://labs.suse.cz/jslaby/bug-968218/
There is also core.s which is a result of:
objdump -d vmlinux-4.4.2-3-default | grep -A 10000 '<update_rq_clock>:'
>core.s
> In my own private configuration, ttwu_stat() doesn't actually touch
> the stack at all - no stack pointer action anywhere except for the
>
> ttwu_stat:
> 1: call __fentry__
> pushq %rbp
> ..
> movq %rsp, %rbp #,
>
> .....
>
> popq %rbp
> ret
>
> but yeah, as Peter says, maybe an exception screwed up %rsp somehow..
Lucky you. My ttwu_stat does a bit more stack save-restoring. But all
seem to be paired:
ffffffff8109f3c0 <ttwu_stat>:
ffffffff8109f3c0: e8 fb ca 60 00 callq ffffffff816abec0
<__fentry__>
ffffffff8109f3c5: 55 push %rbp
ffffffff8109f3c6: 48 89 e5 mov %rsp,%rbp
ffffffff8109f3c9: 41 57 push %r15
ffffffff8109f3cb: 41 56 push %r14
ffffffff8109f3cd: 41 55 push %r13
ffffffff8109f3cf: 41 54 push %r12
ffffffff8109f3d1: 49 c7 c6 80 6e 01 00 mov $0x16e80,%r14
ffffffff8109f3d8: 53 push %rbx
...
ffffffff8109f48c: 5b pop %rbx
ffffffff8109f48d: 41 5c pop %r12
ffffffff8109f48f: 41 5d pop %r13
ffffffff8109f491: 41 5e pop %r14
ffffffff8109f493: 41 5f pop %r15
ffffffff8109f495: 5d pop %rbp
ffffffff8109f496: c3 retq
> I really don't see how it would happen here - that code doesn't look
> particularly odd.
>
> And the fentry code used by the function tracer can certainly screw
> things up, but even that would be hard-pressed to screw up %rbp, since
> the saving of rbp comes *after* fentry. Old pre-__fentry__ gcc
> versions had a much higher likelihood (the whole mcount thing is a
> disaster, but I'm assuming you have a compiler that does __fentry__
> and have CC_USING_FENTRY set?)
Yep, -mfentry in use obviously from the dump above, it is compiled by
gcc 5.3.1 rev231346.
thanks,
--
js
suse labs
next prev parent reply other threads:[~2016-02-26 8:56 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-17 20:37 Linux 4.4.2 Greg KH
2016-02-17 20:37 ` Greg KH
2016-02-25 10:12 ` BUG: unable to handle kernel paging request from pty_write [was: Linux 4.4.2] Jiri Slaby
2016-02-25 18:40 ` Peter Hurley
2016-02-25 19:09 ` Linus Torvalds
2016-02-25 19:23 ` Steven Rostedt
2016-02-26 8:25 ` Jiri Slaby
2016-02-25 20:32 ` Peter Hurley
2016-02-25 20:51 ` Linus Torvalds
2016-02-25 21:32 ` Jiri Slaby
2016-02-25 22:33 ` Peter Hurley
2016-02-26 0:38 ` Peter Hurley
2016-02-26 8:45 ` Jiri Slaby
2016-02-26 0:38 ` Linus Torvalds
2016-02-26 8:56 ` Jiri Slaby [this message]
2016-02-26 9:23 ` Jiri Slaby
2016-02-26 9:50 ` Jiri Slaby
2016-02-26 16:34 ` Greg KH
2016-02-26 17:12 ` Linus Torvalds
2016-02-29 15:45 ` Paolo Bonzini
2016-02-26 17:52 ` Peter Hurley
2016-02-25 21:43 ` Peter Hurley
2016-02-25 22:00 ` Jiri Kosina
2016-02-26 8:31 ` Jiri Slaby
2016-02-26 8:15 ` Jiri Slaby
2016-02-26 18:05 Linus Torvalds
2016-02-26 18:17 ` Borislav Petkov
2016-02-26 18:18 ` Peter Hurley
2016-02-26 19:44 ` Linus Torvalds
2016-02-26 19:59 ` Robert Święcki
2016-02-29 7:39 ` Jiri Slaby
2016-02-29 12:43 ` Henrique de Moraes Holschuh
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