locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling

BugLink: https://bugs.launchpad.net/bugs/1923069
[ Upstream commit 5de2055d31ea88fd9ae9709ac95c372a505a60fa ]

The use_ww_ctx flag is passed to mutex_optimistic_spin(), but the
function doesn't use it. The frequent use of the (use_ww_ctx && ww_ctx)
combination is repetitive.

In fact, ww_ctx should not be used at all if !use_ww_ctx.  Simplify
ww_mutex code by dropping use_ww_ctx from mutex_optimistic_spin() an
clear ww_ctx if !use_ww_ctx. In this way, we can replace (use_ww_ctx &&
ww_ctx) by just (ww_ctx).

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lore.kernel.org/r/20210316153119.13802-2-longman@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 5352ce50a97e309b5bf8cdd2059378b17a8f14ec..2c25b830203cd7be860bdef5ceb856ca065aaceb 100644 (file)
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -636,7 +636,7 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
  */
 static __always_inline bool
 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
-                     const bool use_ww_ctx, struct mutex_waiter *waiter)
+                     struct mutex_waiter *waiter)
 {
        if (!waiter) {
                /*
@@ -712,7 +712,7 @@ fail:
 #else
 static __always_inline bool
 mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
-                     const bool use_ww_ctx, struct mutex_waiter *waiter)
+                     struct mutex_waiter *waiter)
 {
        return false;
 }
@@ -932,6 +932,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
        struct ww_mutex *ww;
        int ret;
 
+       if (!use_ww_ctx)
+               ww_ctx = NULL;
+
        might_sleep();
 
 #ifdef CONFIG_DEBUG_MUTEXES
@@ -939,7 +942,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 #endif
 
        ww = container_of(lock, struct ww_mutex, base);
-       if (use_ww_ctx && ww_ctx) {
+       if (ww_ctx) {
                if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
                        return -EALREADY;
 
@@ -956,10 +959,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
        mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
 
        if (__mutex_trylock(lock) ||
-           mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
+           mutex_optimistic_spin(lock, ww_ctx, NULL)) {
                /* got the lock, yay! */
                lock_acquired(&lock->dep_map, ip);
-               if (use_ww_ctx && ww_ctx)
+               if (ww_ctx)
                        ww_mutex_set_context_fastpath(ww, ww_ctx);
                preempt_enable();
                return 0;
@@ -970,7 +973,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
         * After waiting to acquire the wait_lock, try again.
         */
        if (__mutex_trylock(lock)) {
-               if (use_ww_ctx && ww_ctx)
+               if (ww_ctx)
                        __ww_mutex_check_waiters(lock, ww_ctx);
 
                goto skip_wait;
@@ -1023,7 +1026,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                        goto err;
                }
 
-               if (use_ww_ctx && ww_ctx) {
+               if (ww_ctx) {
                        ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx);
                        if (ret)
                                goto err;
@@ -1036,7 +1039,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                 * ww_mutex needs to always recheck its position since its waiter
                 * list is not FIFO ordered.
                 */
-               if ((use_ww_ctx && ww_ctx) || !first) {
+               if (ww_ctx || !first) {
                        first = __mutex_waiter_is_first(lock, &waiter);
                        if (first)
                                __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
@@ -1049,7 +1052,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                 * or we must see its unlock and acquire.
                 */
                if (__mutex_trylock(lock) ||
-                   (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
+                   (first && mutex_optimistic_spin(lock, ww_ctx, &waiter)))
                        break;
 
                spin_lock(&lock->wait_lock);
@@ -1058,7 +1061,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 acquired:
        __set_current_state(TASK_RUNNING);
 
-       if (use_ww_ctx && ww_ctx) {
+       if (ww_ctx) {
                /*
                 * Wound-Wait; we stole the lock (!first_waiter), check the
                 * waiters as anyone might want to wound us.
@@ -1078,7 +1081,7 @@ skip_wait:
        /* got the lock - cleanup and rejoice! */
        lock_acquired(&lock->dep_map, ip);
 
-       if (use_ww_ctx && ww_ctx)
+       if (ww_ctx)
                ww_mutex_lock_acquired(ww, ww_ctx);
 
        spin_unlock(&lock->wait_lock);