linux-kernel - Re: [RFC] Avoid mutex starvation when optimistic spinning is disabled

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Message-ID: <20160722180309.GB1881@linux-80c1.suse>
Date:	Fri, 22 Jul 2016 11:03:09 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Waiman Long <waiman.long@....com>
Cc:	Jason Low <jason.low2@....com>, imre.deak@...el.com,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [RFC] Avoid mutex starvation when optimistic spinning is disabled

On Fri, 22 Jul 2016, Waiman Long wrote:

>I think making mutex_trylock() fail maybe a bit too far. Do we really 
>have any real workload that cause starvation problem  because of that. 
>Code that does mutex_trylock() in a loop can certainly cause lock 
>starvation, but it is not how mutex_trylock() is supposed to be used. 
>We can't build in safeguard for all the possible abuses of the mutex 
>APIs.

True, and that's actually why I think that 'fixing' the !SPIN_ON_OWNER case
is a bit too far in the first place: most of the archs that will care about
this already have ARCH_SUPPORTS_ATOMIC_RMW. The extra code for dealing with
this is not worth it imo.

Thanks,
Davidlohr