linux-kernel - Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly

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, 10 Oct 2012 16:02:49 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Ivo Sieben <meltedpianoman@...il.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	linux-serial@...r.kernel.org, Alan Cox <alan@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [REPOST] RFC: sched: Prevent wakeup to enter critical section needlessly

> wait_event:
> 
> 	prepare_to_wait(wq)	// takes wq->lock
> 
> 	if (!CONDITION)
> 		schedule();
> 
> Now,
> 
> 	CONDITION = 1;
> 	wake_up(wq);
> 
> at least need the full mb() before lits_empty().

You're right, but it would probably only matter for inlining with LTO
(if the LTO compiler ever decides to do that)

Without that a call should be always enough barrier in practice.

So yes I would add the mb, but most likely it will not make much
difference. Just make sure to comment it.

-Andi
--
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/