linux-kernel - Re: [RFC/PATCH] No get_user/put_user while holding mmap_sem in do_pages

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] [day] [month] [year] [list]

Message-Id: <1228844782.6978.1.camel@twins>
Date:	Tue, 09 Dec 2008 18:46:22 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/PATCH] No get_user/put_user while holding mmap_sem in
 do_pages_stat?

On Tue, 2008-12-09 at 17:47 +0100, Brice Goglin wrote:
> Peter Zijlstra wrote:
> > On Sun, 2008-12-07 at 15:21 +0100, Brice Goglin wrote:
> >   
> >> Andrew Morton wrote:
> >>     
> >>> Was lockdep able to tell you about this in any way?
> >>>   
> >>>       
> >> With CONFIG_PROVE_LOCKING (assuming that it's enough), it doesn't detect
> >> the problem for real. It just says "possible recursive locking detected"
> >> between do_page_fault and sys_move_pages.
> >>     
> >
> > That is real - how much more real do you need a description of a
> > recursive deadlock to be?
> >   
> 
> Well, it's a recursive down_read. It could be ok if we had the guarantee
> that nobody else would be doing down_write in the middle. lockdep only
> complained about this recursive down_read when there was a down_write
> actually causing the deadlock, but it didn't say anything about this
> down_write in the log.
> 
> It would be great if lockdep could say "recursive read-lock is
> deadlocking because this other guy (with its backtrace) took for write
> in the middle". I needed sysrq-t to get this info.

rwsem does not support recursive read-locks, so irrespective of write
side locks, its a bug.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/