linux-ext4 - Re: 2.6.25-git2: BUG: unable to handle kernel paging request at ffffffffffffffff

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20080422010304.GA14994@gondor.apana.org.au>
Date:	Tue, 22 Apr 2008 09:03:04 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-ext4@...r.kernel.org
Subject: Re: 2.6.25-git2: BUG: unable to handle kernel paging request at ffffffffffffffff

On Mon, Apr 21, 2008 at 08:49:58AM -0700, Linus Torvalds wrote:
>
> That is *not* the main problem.
> 
> If you use "rcu_dereference()" on the wrong access, it not only loses the 
> "smp_read_barrier_depends()" (which is a no-op on all sane architectures 
> anyway), but it loses the ACCESS_ONCE() thing *entirely*.

Actually rcu_dereference didn't have ACCESS_ONCE when I did this.
That only appearaed later with the preemptible RCU work.

The original purpose of rcu_dereference was exactly to replace the
explicit barriers that people were using for RCU, nothing more,
nothing less.

Oh and I totally agree that the compiler is going to generate insane
code whenever ACCESS_ONCE is used.  In this case we may have avoided
it by rearranging the code, but in general the introduction of ACCESS_ONCE
in rcu_dereference is likely to have a negative impact on the code
generated.

Remember that "volatile" discussion? I think this is where it all came
from.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html