linux-kernel - Re: [PATCH 00/17] Backport rt/deadline crash and the ardous story of FUTEX_UNLOCK

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Date:   Fri, 14 Dec 2018 08:36:46 +0100
From:   Henrik Austad <henrik@...tad.us>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Henrik Austad <haustad@...co.com>,
        Peter Zijlstra <peterz@...radead.org>, juri.lelli@....com,
        bigeasy@...utronix.de, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jdesfossez@...icios.com,
        dvhart@...radead.org, bristot@...hat.com,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 00/17] Backport rt/deadline crash and the ardous story of
 FUTEX_UNLOCK_PI to 4.4

On Fri, Dec 14, 2018 at 08:18:26AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Nov 19, 2018 at 12:27:21PM +0100, Henrik Austad wrote:
> > On Fri, Nov 09, 2018 at 11:35:31AM +0100, Henrik Austad wrote:
> > > On Fri, Nov 09, 2018 at 11:07:28AM +0100, Henrik Austad wrote:
> > > > From: Henrik Austad <haustad@...co.com>
> > > > 
> > > > Short story:
> > > 
> > > Sorry for the spam, it looks like I was not very specific in /which/ 
> > > version I targeted this to, as well as not providing a full Cc-list for the 
> > > cover-letter.
> > 
> > Gentle prod. I realize this was sent out just before plumbers and that 
> > people had pretty packed agendas, so a small nudge to gain a spot closer to 
> > the top of the inbox :)
> > 
> > This series has now been running on an arm64 system for 9 days without any 
> > issues and pi_stress showed a dramatic improvement from ~30 seconds and up 
> > to several ours (it finally deadlocked at 3.9e9 inversions).
> > 
> > I'd greatly appreciate if someone could give the list of patches a quick 
> > glance to verify that I got all the required patches and then if it could 
> > be added to 4.4.y.

Hi Greg,

> This is a really intrusive series of patches, and without some testing
> and verification by others, I am really reluctant to take these patches.

Yes I know, they are intrusive, and they touch core parts of the kernel in 
interesting ways.

I completely agree with the need for testing, and I do not _expect_ these 
pathces to be merged. It was a "this was useful for us, it is probably 
useful for others" kind of series.

Perhaps it is not that many others out there using pi_futex shared between 
a sched_rr thread and a sched_deadline thread, which is how you back 
yourself into this corner.

> Why not just move to the 4.9.y tree, or better yet, 4.19.y to resolve
> this issue for your systems?

That would indeed be the best solution, but vendor will not update kernel 
past 4.4 for this particular SoC, so we have no way of moving this to a 
later kernel :(

Anyway, I'm happy to carry these in our local tree for our own use. If 
something pops up in our internal testing requiring update to the series, 
I'll send an update for others to see should they experience the same 
issue. :)

Thanks for the reply!

-- 
Henrik Austad

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