[PATCH AUTOSEL 5.4 23/24] locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling

From: Sasha Levin
Date: Thu Mar 25 2021 - 07:35:34 EST


From: Waiman Long <longman@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
Link: https://lore.kernel.org/r/20210316153119.13802-2-longman@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/locking/mutex.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 468a9b8422e3..07a9f9f46e03 100644
--- 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 @@ mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
#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 @@ __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 && ww_ctx)
+ if (ww_ctx)
ww_mutex_lock_acquired(ww, ww_ctx);

spin_unlock(&lock->wait_lock);
--
2.30.1