linux-kernel - Re: 2.6.19-rc1-mm1

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:	Wed, 11 Oct 2006 13:23:06 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Michal Piotrowski <michal.k.k.piotrowski@...il.com>
Cc:	Neil Brown <neilb@...e.de>, Andrew Morton <akpm@...l.org>,
	Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: 2.6.19-rc1-mm1


> > blocking_notifier_call_chain is
> >         down_read(&nh->rwsem);
> >         ret = notifier_call_chain(&nh->head, val, v);
> >         up_read(&nh->rwsem);
> >
> > and so holds ->rwsem while calling the callback.
> > So the locking sequence ends up as:
> >
> >  down_read(&cpu_chain.rwsem);
> >  mutex_lock(&workqueue_mutex);
> >  up_read(&cpu_chain.rwsem);
> >
> >  down_read(&cpu_chain.rwsem);
> >  mutex_unlock(&workqueue_mutex);
> >  up_read(&workqueue_mutex);
> >
> > and lockdep doesn't seem to like this.  It sees workqueue_mutex
> > claimed while cpu_chain.rwsem is held. and then it sees
> > cpu_chain.rwsem claimed while workqueue_mutex is held, which looks a
> > bit like a class ABBA deadlock.
> > Of course because it is a 'down_read' rather than a 'down', it isn't
> > really a dead lock.

ok can you explain to me why "down_read" doesn't make this a deadlock
while "down" would make it a deadlock? I have trouble following your
reasoning.....

(remember that rwsems are strictly fair)


-
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/