linux-kernel - Re: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup

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]

Message-ID: <1271425881.4807.2319.camel@twins>
Date:	Fri, 16 Apr 2010 15:51:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH 01/13] powerpc: Add rcu_read_lock() to gup_fast()
 implementation

On Thu, 2010-04-15 at 07:28 -0700, Paul E. McKenney wrote:
> On Wed, Apr 14, 2010 at 03:51:50PM +0200, Peter Zijlstra wrote:
> > On Mon, 2010-04-12 at 20:43 -0700, Paul E. McKenney wrote:
> > > > So we might have to support the interrupt assumption, at least in some
> > > > form, with those guys...
> > > 
> > > One way to make the interrupt assumption official is to use
> > > synchronize_sched() rather than synchronize_rcu().
> > 
> > Well, call_rcu_sched() then, because the current usage is to use
> > call_rcu() to free the page directories.
> > 
> > Paul, here is a call_rcu_sched() available in kernel/rcutree.c, but am I
> > right in reading that code that that would not be available for
> > preemptible RCU?
> 
> Both call_rcu_sched() and call_rcu() are always there for you.  ;-)
> 
> o	If CONFIG_TREE_RCU (or CONFIG_TINY_RCU), they both have the same
> 	implementation.
> 
> o	If CONFIG_TREE_PREEMPT_RCU, call_rcu_sched() is preemptible and
> 	call_rcu() is not.

(The reverse I suspect?)

> Of course, with call_rcu_sched(), the corresponding RCU read-side critical
> sections are non-preemptible.  Therefore, in CONFIG_PREEMPT_RT, these
> read-side critical sections must use raw spinlocks.

OK, so if we fully remove CONFIG_TREE_PREEMPT_RCU (defaulting to y),
rename all the {call_rcu, rcu_read_lock, rcu_read_unlock,
synchronize_rcu} functions to {*}_preempt and then add a new
CONFIG_PREEMPT_RCU that simply maps {*} to either {*}_sched or
{*}_preempt, we've basically got what I've been asking for for a while,
no?

> Can the code in question accommodate these restrictions?

Yes, that should do just fine I think.
--
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/