linux-kernel - Re: [RFC 0/4] use rcu_read_lock() during module list walk

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: <20150731172246.GB25159@twins.programming.kicks-ass.net>
Date:	Fri, 31 Jul 2015 19:22:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	tglx@...utronix.de
Subject: Re: [RFC 0/4] use rcu_read_lock() during module list walk

On Fri, Jul 31, 2015 at 07:08:04PM +0200, Sebastian Andrzej Siewior wrote:
> Hi Peter,
> 
> this series was made before I noticed that you introduced a RB tree for
> lookup but the old way still remains under !CONFIG_MODULES_TREE_LOOKUP.

> In the old way the caller had preempt_disable() while invoking
> list_for_each_safe_rcu() which is (according to the RCU checklist) not a
> substitute for rcu_readlock().

This is true. preempt_disable() != rcu_read_lock().

> With your CONFIG_MODULES_TREE_LOOKUP I fail to understand what blocks
> free_module() until all mod_find() callers have dropped their refrence to
> the obtained struct mod. We had synchronize_sched() in RCU case.

We still have synchronize_sched(), but that is not RCU, that is
RCU-sched, and rcu_read_lock_sched() == preempt_disable() (+- some
debugging bits).

The code used to be broken in this regard, see 0be964be0d45 ("module:
Sanitize RCU usage and locking"), that fixed things to be consistent.
--
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/