Date: Thu, 12 Feb 2015 15:02:48 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, peterz@infradead.org,
        torvalds@linux-foundation.org, konrad.wilk@oracle.com,
        pbonzini@redhat.com, paulmck@linux.vnet.ibm.com, waiman.long@hp.com,
        davej@redhat.com, x86@kernel.org, jeremy@goop.org,
        paul.gortmaker@windriver.com, ak@linux.intel.com, jasowang@redhat.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        xen-devel@lists.xenproject.org, riel@redhat.com,
        borntraeger@de.ibm.com, akpm@linux-foundation.org,
        a.ryabinin@samsung.com, sasha.levin@oracle.com, dave@stgolabs.net
Subject: Re: [PATCH V3] x86 spinlock: Fix memory corruption on completing
	completions
Message-ID: <20150212140248.GA11050@redhat.com>
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Damn, sorry for noise, forgot to mention...

On 02/12, Raghavendra K T wrote:
>
> +static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
> +							__ticket_t head)
> +{
> +	if (head & TICKET_SLOWPATH_FLAG) {
> +		arch_spinlock_t old, new;
> +
> +		old.tickets.head = head;
> +		new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
> +		old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
> +		new.tickets.tail = old.tickets.tail;
> +
> +		/* try to clear slowpath flag when there are no contenders */
> +		cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
> +	}
> +}

...

> +clear_slowpath:
> +	if (TICKET_SLOWPATH_FLAG)
> +		__ticket_check_and_clear_slowpath(lock, inc.head);

I think you can remove this "if (TICKET_SLOWPATH_FLAG)" check. If it is
defined as zero, gcc should optimize out the code under "if (head & 0)".

But this is purely cosmetic and subjective, feel free to ignore.

Oleg.

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