linux-kernel - Re: deadlock in scheduler enabling HRTICK feature

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:	Fri, 28 Jun 2013 11:09:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Ahern <dsahern@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: deadlock in scheduler enabling HRTICK feature

On Thu, Jun 27, 2013 at 04:28:57PM -0600, David Ahern wrote:
> On 6/27/13 4:43 AM, Peter Zijlstra wrote:
> >On Wed, Jun 26, 2013 at 10:46:33AM -0600, David Ahern wrote:
> >>On 6/26/13 1:05 AM, Peter Zijlstra wrote:
> >>>>What is the expectation that the feature provides? not a whole lot of
> >>>>documentation on it. I walked down the path wondering if it solved an odd
> >>>>problem we are seeing with the CFS in 2.6.27 kernel.
> >>>
> >>>Its supposed to use hrtimers for slice expiry instead of the regular tick.
> >>
> >>So theoretically CPU bound tasks would get preempted sooner? That was my
> >>guess/hope anyways.
> >
> >Doth the below worketh?
> 
> It doth.
> 
> Usually make -j 8 for a kernel build in a VM would lock it up pretty
> quickly. With the patch I was able to run full builds multiple times.

Good!

> As for the solution you are avoiding the nesting by not waking up the
> softirq daemon.

Yah! :-) Obviously doing a wakeup while holding scheduler locks isn't going to
work out well. And the only reason we really need that pesky softirq nonsense
is when we accidentally schedule a timer that's already expired; in that case
we'll run it from sirq context.

We don't care about missing events like that; there's always the actual tick
for backup.

I suppose I'd better go write a Changelog and properly submit the patch :-)
--
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/