[tip: locking/urgent] locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling

tip-bot2 for Waiman Long
2021-03-17T12:39:15Z

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID: 5de2055d31ea88fd9ae9709ac95c372a505a60fa
Gitweb: https://git.kernel.org/tip/5de2055d31ea88fd9ae9709ac95c372a505a60fa
Author: Waiman Long <longman@redhat.com>
AuthorDate: Tue, 16 Mar 2021 11:31:16 -04:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 17 Mar 2021 09:56:44 +01:00

locking/ww_mutex: Simplify use_ww_ctx & ww_ctx handling

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
---
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 adb9350..622ebdf 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -626,7 +626,7 @@ 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) {
/*
@@ -702,7 +702,7 @@ 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;
}
@@ -922,6 +922,9 @@ __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
@@ -929,7 +932,7 @@ __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;

@@ -946,10 +949,10 @@ __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;
@@ -960,7 +963,7 @@ __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;
@@ -1013,7 +1016,7 @@ __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;
@@ -1026,7 +1029,7 @@ __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);
@@ -1039,7 +1042,7 @@ __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);
@@ -1048,7 +1051,7 @@ __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.
@@ -1068,7 +1071,7 @@ 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);