From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jiri Slaby <jslaby@suse.cz>
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: Thu, 25 Feb 2016 16:38:13 -0800 [thread overview]
Message-ID: <CA+55aFzQzCKhX73bUYwNMK8Dd9ECtmav8u7ds2aXKjEo7DV3Gg@mail.gmail.com> (raw)
In-Reply-To: <56CF72EA.9040009@suse.cz>
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?
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..
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?)
Linus
next prev parent reply other threads:[~2016-02-26 0:38 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 [this message]
2016-02-26 8:56 ` Jiri Slaby
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CA+55aFzQzCKhX73bUYwNMK8Dd9ECtmav8u7ds2aXKjEo7DV3Gg@mail.gmail.com \
--to=torvalds@linux-foundation.org \
--cc=akpm@linux-foundation.org \
--cc=gregkh@linuxfoundation.org \
--cc=jslaby@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=lwn@lwn.net \
--cc=peter@hurleysoftware.com \
--cc=rostedt@goodmis.org \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).