On Thu, Dec 01, 2016 at 03:06:47PM +0100, Nicolai Hähnle wrote:
> @@ -640,10 +640,11 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
> struct mutex_waiter waiter;
> unsigned long flags;
> bool first = false;
> - struct ww_mutex *ww;
> int ret;
>
> - if (use_ww_ctx) {
> + if (use_ww_ctx && ww_ctx) {
> + struct ww_mutex *ww;
> +
> ww = container_of(lock, struct ww_mutex, base);
> if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
> return -EALREADY;
So I don't see the point of removing *ww from the function scope, we can
still compute that container_of() even if !ww_ctx, right? That would
safe a ton of churn below, adding all those struct ww_mutex declarations
and container_of() casts.
(and note that the container_of() is a fancy NO-OP because base is the
first member).
> @@ -656,8 +657,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
> mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
> /* got the lock, yay! */
> lock_acquired(&lock->dep_map, ip);
> - if (use_ww_ctx)
> + if (use_ww_ctx && ww_ctx) {
> + struct ww_mutex *ww;
> +
> + ww = container_of(lock, struct ww_mutex, base);
> ww_mutex_set_context_fastpath(ww, ww_ctx);
> + }
> preempt_enable();
> return 0;
> }
> @@ -702,7 +707,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
> goto err;
> }
>
> - if (use_ww_ctx && ww_ctx->acquired > 0) {
> + if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
> ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
> if (ret)
> goto err;
> @@ -742,8 +747,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
> /* got the lock - cleanup and rejoice! */
> lock_acquired(&lock->dep_map, ip);
>
> - if (use_ww_ctx)
> + if (use_ww_ctx && ww_ctx) {
> + struct ww_mutex *ww;
> +
> + ww = container_of(lock, struct ww_mutex, base);
> ww_mutex_set_context_slowpath(ww, ww_ctx);
> + }
>
> spin_unlock_mutex(&lock->wait_lock, flags);
> preempt_enable();
All that then reverts to:
- if (use_ww_ctx)
+ if (use_ww_ctx && ww_ctx)
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