linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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]

Date:	Thu, 16 Apr 2015 10:04:17 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	Tom Gundersen <teg@...m.no>, Havoc Pennington <hp@...ox.com>,
	Rik van Riel <riel@...hat.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

On Thu, Apr 16, 2015 at 8:01 AM, David Herrmann <dh.herrmann@...il.com> wrote:
> Hi
>
> On Thu, Apr 16, 2015 at 4:34 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> Whose memcg does the pool use?
>
> The pool-owner's (i.e., the receiver's).
>
>> If it's the receiver's, and if the
>> receiver can configure a memcg, then it seems that even a single
>> receiver could probably cause the sender to block for an unlimited
>> amount of time.
>
> How? Which of those calls can block? I don't see how that can happen.

I admit I don't fully understand memcg, but vfs_iter_write is
presumably going to need to get write access to the target pool page,
and that, in turn, will need that page to exist in memory and to be
writable, which may need to page it in and/or allocate a page.  If
that uses the receiver's memcg (as it should), then the receiver can
make it block.  Even if it doesn't use the receiver's memcg, it can
trigger direct reclaim, I think.

--Andy
--
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/