From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing
	completions
Date: Thu, 12 Feb 2015 14:37:07 +0100
Message-ID: <20150212133707.GA10232@redhat.com>
References: <1423741647-2156-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
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To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: jeremy@goop.org, kvm@vger.kernel.org, peterz@infradead.org, virtualization@lists.linux-foundation.org, paul.gortmaker@windriver.com, hpa@zytor.com, ak@linux.intel.com, a.ryabinin@samsung.com, x86@kernel.org, borntraeger@de.ibm.com, mingo@redhat.com, xen-devel@lists.xenproject.org, paulmck@linux.vnet.ibm.com, riel@redhat.com, konrad.wilk@oracle.com, dave@stgolabs.net, sasha.levin@oracle.com, davej@redhat.com, tglx@linutronix.de, waiman.long@hp.com, linux-kernel@vger.kernel.org, pbonzini@redhat.com, akpm@linux-foundation.org, torvalds@linux-foundation.org
List-Id: virtualization@lists.linuxfoundation.org

On 02/12, Raghavendra K T wrote:
>
> @@ -772,7 +773,8 @@ __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
>  	 * check again make sure it didn't become free while
>  	 * we weren't looking.
>  	 */
> -	if (ACCESS_ONCE(lock->tickets.head) == want) {
> +	head = ACCESS_ONCE(lock->tickets.head);
> +	if (__tickets_equal(head, want)) {
>  		add_stats(TAKEN_SLOW_PICKUP, 1);

While at it, perhaps it makes sense to s/ACCESS_ONCE/READ_ONCE/ but this
is cosmetic.

We also need to change another user of enter_slow_path, xen_lock_spinning()
in arch/x86/xen/spinlock.c.

Other than that looks correct at first glance... but this is up to
maintainers.

Oleg.