linux-kernel - Re: [Nbd] [PATCH 1/1] NBD: allow nbd to be used locally

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 for Android: free password hash cracker in your pocket

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

Date:	Mon, 24 Mar 2008 22:58:47 +0100
From:	Pavel Machek <pavel@....cz>
To:	Wouter Verhelst <w@...r.be>
Cc:	Paul Clements <paul.clements@...eleye.com>,
	nbd-general@...ts.sourceforge.net,
	Laurent Vivier <Laurent.Vivier@...l.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [Nbd] [PATCH 1/1] NBD: allow nbd to be used locally

Hi!

> > >>> This patch allows a Network Block Device to be mounted locally 
> > >>> (nbd-client to nbd-server over 127.0.0.1).
> > >>>
> > >>> It creates a kthread to avoid the deadlock described in NBD tools 
> > >>> documentation. So, if nbd-client hangs waiting for pages, the kblockd 
> > >>> thread can continue its work and free pages.
> > >>
> > >> What happens if your new kthread blocks on memory allocation?
> > >
> > > Well, we expect that. The reason for the new thread is so that it hangs, 
> > > rather than kblockd hanging (which on a UP system brings all I/O to a 
> > > halt). As long as kblockd can continue making progress, we eventually free 
> > > up memory and then NBD can finish its requests, too.
> > 
> > ....unless all the memory is in dirty buffers for nbd, and nbd server
> > is swapped out or something?
> 
> Note that I'm not a kernel hacker, so might be terribly mistaken here...
> 
> but I feel I should point out that this patch solves the issue that no
> two block devices can flush their dirty buffers at the same time.
> Without this patch, you can't write to a _filesystem_ on an NBD device
> if that's connected to a server on the localhost. You are correct that
> this does not solve the deadlock in swapping to NBD devices, but that's
> not the only existing deadlock issue in NBD to localhost...

Same issue with swapping probably exists with dirty block
writeout... swapoff -a, and filesystem becomes very similar to swap.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
pomozte zachranit klanovicky les:  http://www.ujezdskystrom.info/
--
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/