Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity

From	Juri Lelli <juri.lelli@arm.com>
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity
Date	2016-06-28 11:10 +0200
Message-ID	<rOXbP-4Tg-3@gated-at.bofh.it> (permalink)
References	(1 earlier) <rHvNn-7ix-7@gated-at.bofh.it> <rK0tH-7VX-5@gated-at.bofh.it> <rK2vv-NN-11@gated-at.bofh.it> <rKdqV-7W8-5@gated-at.bofh.it> <rODPP-9s-3@gated-at.bofh.it>
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On 27/06/16 14:23, Peter Zijlstra wrote:
> On Wed, Jun 15, 2016 at 08:25:07AM +0100, Juri Lelli wrote:
> > I guess it's not that likely, but yes it could potentially happen that a
> > waiter is optimistically spinning, depletes its runtime, gets throttled
> > and then replenished when still spinning. Maybe it doesn't really make
> > sense continuing spinning in this situation, but I guess things get
> > really complicated. :-/
> > 
> > Anyway, as said, I think this patch is OK. Maybe we want to add a
> > comment just to remember what situation can cause an issue if we don't
> > do this? Patch changelog would be OK as well for such a comment IMHO.
> 
> 
> OK, so I went to write a simple comment and ended up with the below :/
> 
> While writing the comment I noticed two issues:
> 
>  - we update the waiter order fields while the entry is still enqueued
>    on the pi_waiters tree, which is also sorted by these exact fields.
> 
>  - another one of these pure ->prio comparisons
> 
> Please double check, there be dragons here.
> 

Reviewed-and-tested-by: Juri Lelli <juri.lelli@arm.com>

And, FWIW, you can obviously keep this if you are going to squash this
into 8/8.

Best,

- Juri

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Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity Peter Zijlstra <peterz@infradead.org> - 2016-06-27 14:30 +0200
  Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity Thomas Gleixner <tglx@linutronix.de> - 2016-06-27 14:50 +0200
  Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity Juri Lelli <juri.lelli@arm.com> - 2016-06-28 11:10 +0200

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