linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
To: Mike Krinkin <krinkin.m.u@gmail.com>
Cc: <akpm@linux-foundation.org>, <linux-kernel@vger.kernel.org>
Subject: Re: CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled
Date: Mon, 1 Feb 2016 18:10:38 +0300	[thread overview]
Message-ID: <56AF756E.9080102@virtuozzo.com> (raw)
In-Reply-To: <20160130003645.GA30158@kmu-tp-x230>

On 01/30/2016 03:36 AM, Mike Krinkin wrote:
> Hi,
> 
> option CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled,
> i. e kernel with CONFIG_UBSAN_ALIGNMENT fails to load without even any
> error message.
> 
> The problem is that ubsan callbacks use spinlocks and might be called
> before lockdep is initialized. Particularly this line in the
> reserve_ebda_region function causes problem:
> 
> lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
> 
> If i put lockdep_init() before reserve_ebda_region call in
> x86_64_start_reservations kernel loads well. Since CONFIG_UBSAN_ALIGNMENT
> isn't useful for x86 anyway it might be better to disable this option for
> x86 arch?
> 


Alignment checks could be useful even on x86, because there are unaligned accesses in generic code.
I think we can disable alignment instrumentation for arch/x86 directory only.

  reply	other threads:[~2016-02-01 15:09 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-30  0:36 CONFIG_UBSAN_ALIGNMENT breaks x86-64 kernel with lockdep enabled Mike Krinkin
2016-02-01 15:10 ` Andrey Ryabinin [this message]
2016-02-01 22:21   ` Andrew Morton
2016-02-02 16:18     ` Andrey Ryabinin
2016-02-02 21:18       ` Andrew Morton

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=56AF756E.9080102@virtuozzo.com \
    --to=aryabinin@virtuozzo.com \
    --cc=akpm@linux-foundation.org \
    --cc=krinkin.m.u@gmail.com \
    --cc=linux-kernel@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).