Date: Tue, 28 Jan 2014 21:54:06 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Jason Low <jason.low2@hp.com>
Cc: mingo@redhat.com, paulmck@linux.vnet.ibm.com, Waiman.Long@hp.com,
        torvalds@linux-foundation.org, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, riel@redhat.com,
        akpm@linux-foundation.org, davidlohr@hp.com, hpa@zytor.com,
        andi@firstfloor.org, aswin@hp.com, scott.norton@hp.com,
        chegu_vinod@hp.com
Subject: Re: [RFC][PATCH v2 4/5] mutex: Disable preemtion between modifying
 lock->owner and locking/unlocking mutex
Message-ID: <20140128205406.GI11314@laptop.programming.kicks-ass.net>
References: <1390936396-3962-1-git-send-email-jason.low2@hp.com>
 <1390936396-3962-5-git-send-email-jason.low2@hp.com>
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On Tue, Jan 28, 2014 at 11:13:15AM -0800, Jason Low wrote:
> This RFC patch disables preemption between modifying lock->owner and
> locking/unlocking the mutex lock. This prevents situations where the owner
> can preempt between those 2 operations, which causes optimistic spinners to
> be unable to check if lock->owner is not on CPU. As mentioned in the
> thread for this v1 patchset, disabling preemption is a cheap operation.

In that same thread it was also said that this wasn't really an issue at
all. So what is the justification?

The patch is rather hideous.
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