linux-kernel - Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline

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: <20151105164951.GI3604@twins.programming.kicks-ass.net>
Date:	Thu, 5 Nov 2015 17:49:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@....com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next
 node cacheline

On Thu, Nov 05, 2015 at 11:42:27AM -0500, Waiman Long wrote:
> If we observe next, we will observe val != tail sooner or later. It is not
> possible for it to clear the tail code in the lock. The tail xchg will
> guarantee that.
> 
> Another alternative is to do something like
> 
> +    if (!next)
>          while (!(next = READ_ONCE(node->next)))
>             cpu_relax();
> 

Yes maybe, although the main reason I fell over this was because it was
a separate change (and not mentioned in the Changelog).

Although the above would need braces (per CodingStyle), so:

	if (!next) {
		while (!(next = READ_ONCE(node->next)))
			cpu_relax();
	}



--
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/