Hello,
On Mon, Nov 04, 2013 at 11:37:13PM +0000, Tim Chen wrote:
> The following changes are made to enable mcs_spinlock.h file to be
> widely included in other files without causing problem:
>
> 1) Include a number of prerequisite header files and define
> arch_mutex_cpu_relax(), if not previously defined.
> 2) Separate out mcs_spin_lock() into a mcs_spinlock.c file.
> 3) Make mcs_spin_unlock() an inlined function.
[...]
> +void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
> +{
> + struct mcs_spinlock *prev;
> +
> + /* Init node */
> + node->locked = 0;
> + node->next = NULL;
> +
> + prev = xchg(lock, node);
> + if (likely(prev == NULL)) {
> + /* Lock acquired */
> + node->locked = 1;
> + return;
> + }
> + ACCESS_ONCE(prev->next) = node;
> + smp_wmb();
> + /* Wait until the lock holder passes the lock down */
> + while (!ACCESS_ONCE(node->locked))
> + arch_mutex_cpu_relax();
> +}
You have the barrier in a different place than the version in the header
file; is this intentional?
Also, why is an smp_wmb() sufficient (as opposed to a full smp_mb()?). Are
there restrictions on the types of access that can occur in the critical
section?
Will
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