Re: [PATCH v2] locking/mutex: Prevent lock starvation when spinning is enabled

Jason Low
2016-08-11T02:39:30Z

On Wed, 2016-08-10 at 11:44 -0700, Jason Low wrote:
> @@ -917,11 +976,12 @@ EXPORT_SYMBOL(mutex_trylock);
> int __sched
> __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> {
> - int ret;
> + int ret = 1;
>
> might_sleep();
>
> - ret = __mutex_fastpath_lock_retval(&lock->base.count);
> + if (!need_yield_to_waiter(lock))
> + ret = __mutex_fastpath_lock_retval(&lock->base.count);
>
> if (likely(!ret)) {
> ww_mutex_set_context_fastpath(lock, ctx);
> @@ -935,11 +995,12 @@ EXPORT_SYMBOL(__ww_mutex_lock);
> int __sched
> __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
> {
> - int ret;
> + int ret = 1;
>
> might_sleep();
>
> - ret = __mutex_fastpath_lock_retval(&lock->base.count);
> + if (!need_yield_to_waiter(lock))

And we would need to pass &lock->base instead of lock since lock is
struct ww_mutex * here.