linux-kernel - Re: [PATCH] sched: correct testing need_resched in mutex_spin_on

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Message-ID: <1307457646.2322.273.camel@twins>
Date:	Tue, 07 Jun 2011 16:40:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: correct testing need_resched in
 mutex_spin_on_owner()

On Tue, 2011-06-07 at 22:36 +0800, Hillf Danton wrote:

> If you are right, the following comment also in __mutex_lock_common()
> 
> 	for (;;) {
> 		struct task_struct *owner;
> 
> 		/*
> 		 * If there's an owner, wait for it to either
> 		 * release the lock or go to sleep.
> 		 */
> 		owner = ACCESS_ONCE(lock->owner);
> 		if (owner && !mutex_spin_on_owner(lock, owner))
> 			break;
> 
> looks misleading too, but if owner is on this CPU, for what does we wait?

huh, wtf!? it cannot be on this cpu, if it was we wouldn't be running
the above code but whatever owner was doing.

So my argument was, it cannot be on this cpu, therefore, by checking it
is on a cpu, we check its on a different cpu.

And I really don't see how any of that is related to the above.
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