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Date:   Thu, 18 Apr 2019 10:39:39 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Davidlohr Bueso <dave@stgolabs.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        huang ying <huang.ying.caritas@gmail.com>
Subject: Re: [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on_owner()
 return owner state
Message-ID: <20190418083939.GU12232@hirez.programming.kicks-ass.net>
References: <20190413172259.2740-1-longman@redhat.com>
 <20190413172259.2740-9-longman@redhat.com>
 <20190417124101.GE4038@hirez.programming.kicks-ass.net>
 <20190417124759.GT14281@hirez.programming.kicks-ass.net>
 <e9e3c08c-a153-ad38-059e-98b1b212e11f@redhat.com>
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On Wed, Apr 17, 2019 at 02:29:02PM -0400, Waiman Long wrote:
> On 04/17/2019 08:47 AM, Peter Zijlstra wrote:
> >>
> >> enum owner_state {
> >> 	OWNER_NULL		= 1 << 0,
> >> 	OWNER_WRITER		= 1 << 1,
> >> 	OWNER_READER		= 1 << 2,
> >> 	OWNER_NONSPINNABLE	= 1 << 3,
> >> };
> >> #define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER)
> > Hmm, we should not spin on OWNER_NULL. Or at least not mixed in with the
> > patch that changes the shape of all this. That should go in the RT
> > thingy patch, which comes after this.
> 
> We do spin on OWNER_NULL right now, not in rwsem_spin_on_owner() but in
> the main rwsem_optimistic_spin() function.
> 
> RT task will quit if owner is NULL.

Yeah, I figured it out eventually :-)