kernel/z_swap: Remove on-stack dummy spinlock

Andy Ross · nashif · commit 1d51e888d88c · 2021-02-11T14:47:40.000-05:00
The z_swap_unlocked() function used a dummy spinlock for simplicity.
But this runs afouls of checking for stack-resident spinlocks
(forbidden when KERNEL_COHERENCE is set).  And it's executing needless
code to release the lock anyway.  Replace with a compile time NULL,
which will improve performance, correctness and code size.

Signed-off-by: Andy Ross &lt;andrew.j.ross@intel.com&gt;
diff --git a/kernel/include/kswap.h b/kernel/include/kswap.h
@@ -68,7 +68,7 @@ static ALWAYS_INLINE unsigned int do_swap(unsigned int key,
 
 	z_check_stack_sentinel();
 
-	if (is_spinlock) {
+	if (is_spinlock && lock != NULL) {
 		k_spin_release(lock);
 	}
 
@@ -136,10 +136,7 @@ static inline int z_swap(struct k_spinlock *lock, k_spinlock_key_t key)
 
 static inline void z_swap_unlocked(void)
 {
-	struct k_spinlock lock = {};
-	k_spinlock_key_t key = k_spin_lock(&lock);
-
-	(void) z_swap(&lock, key);
+	(void) do_swap(arch_irq_lock(), NULL, 1);
 }
 
 #else /* !CONFIG_USE_SWITCH */

Original file line number	Diff line number	Diff line change
`@@ -68,7 +68,7 @@ static ALWAYS_INLINE unsigned int do_swap(unsigned int key,`
`68`	`68`
`69`	`69`	`z_check_stack_sentinel();`
`70`	`70`
`71`		`- if (is_spinlock) {`
	`71`	`+ if (is_spinlock && lock != NULL) {`
`72`	`72`	`k_spin_release(lock);`
`73`	`73`	`}`
`74`	`74`
`@@ -136,10 +136,7 @@ static inline int z_swap(struct k_spinlock *lock, k_spinlock_key_t key)`
`136`	`136`
`137`	`137`	`static inline void z_swap_unlocked(void)`
`138`	`138`	`{`
`139`		`- struct k_spinlock lock = {};`
`140`		`- k_spinlock_key_t key = k_spin_lock(&lock);`
`141`		`-`
`142`		`- (void) z_swap(&lock, key);`
	`139`	`+ (void) do_swap(arch_irq_lock(), NULL, 1);`
`143`	`140`	`}`
`144`	`141`
`145`	`142`	`#else /* !CONFIG_USE_SWITCH */`