linux-kernel - Re: linux-next: build failure after merge of the tip tree

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:	Mon, 20 Jan 2014 12:05:42 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Len Brown <lenb@...nel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-next@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the tip tree

On Mon, Jan 20, 2014 at 03:00:29AM -0800, H. Peter Anvin wrote:
> On 01/20/2014 01:55 AM, Peter Zijlstra wrote:
> > 
> > Ok, so I still don't get the problem of enabling interrupts early.
> > 
> > If we enable them early we can get interrupts; which afaict fall into
> > two groups, those that do and do not set NEED_RESCHED.
> > 
> > For those that do not set NEED_RESCHED, we'd have woken from MWAIT/HLT
> > and looped right back into it, so receiving those early -- before
> > actually calling MWAIT/HLT seems like a NO-OP.
> 
> The description for commit d331e739f5ad seems to indicate otherwise:
> 
>     Idle callbacks has some races when enter_idle() sets isidle and
> subsequent
>     interrupts that can happen on that CPU, before CPU goes to idle. Due
> to this,
>     an IDLE_END can get called before IDLE_START. To avoid these races,
> disable
>     interrupts before enter_idle and make sure that all idle routines do not
>     enable interrupts before entering idle.
> 
> This implies to me that once we have set isidle, if we take an interrupt
> we *have* to drop out of the idle routine.

I don't think that applies anymore; the generic idle loop calls
arch_cpu_idle_enter() before calling arch_cpu_idle() where we would do
the enable.

So in that sense its impossible to get arch_cpu_idle_exit() -- or rather
exit_idle() as called from the interrupts -- to happen before
arch_cpu_idle_enter().
--
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/