mem_slab: move global lock to per slab lock

This avoids contention between unrelated slabs and allows for
userspace accessible slabs when located in memory partitions.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

include/kernel.h

@@ -4724,6 +4724,7 @@ __syscall size_t k_pipe_write_avail(struct k_pipe *pipe);
 
 struct k_mem_slab {
 	_wait_q_t wait_q;
+	struct k_spinlock lock;
 	uint32_t num_blocks;
 	size_t block_size;
 	char *buffer;
@@ -4740,6 +4741,7 @@ struct k_mem_slab {
 #define Z_MEM_SLAB_INITIALIZER(obj, slab_buffer, slab_block_size, \
 			       slab_num_blocks) \
 	{ \
+	.lock = {}, \
 	.wait_q = Z_WAIT_Q_INIT(&obj.wait_q), \
 	.num_blocks = slab_num_blocks, \
 	.block_size = slab_block_size, \

kernel/mem_slab.c

@@ -15,8 +15,6 @@
 #include <init.h>
 #include <sys/check.h>
 
-static struct k_spinlock lock;
-
 #ifdef CONFIG_OBJECT_TRACING
 struct k_mem_slab *_trace_list_k_mem_slab;
 #endif	/* CONFIG_OBJECT_TRACING */
@@ -88,6 +86,7 @@ int k_mem_slab_init(struct k_mem_slab *slab, void *buffer,
 	slab->block_size = block_size;
 	slab->buffer = buffer;
 	slab->num_used = 0U;
+	slab->lock = (struct k_spinlock) {};
 
 #ifdef CONFIG_MEM_SLAB_TRACE_MAX_UTILIZATION
 	slab->max_used = 0U;
@@ -108,7 +107,7 @@ out:
 
 int k_mem_slab_alloc(struct k_mem_slab *slab, void **mem, k_timeout_t timeout)
 {
-	k_spinlock_key_t key = k_spin_lock(&lock);
+	k_spinlock_key_t key = k_spin_lock(&slab->lock);
 	int result;
 
 	if (slab->free_list != NULL) {
@@ -128,21 +127,21 @@ int k_mem_slab_alloc(struct k_mem_slab *slab, void **mem, k_timeout_t timeout)
 		result = -ENOMEM;
 	} else {
 		/* wait for a free block or timeout */
-		result = z_pend_curr(&lock, key, &slab->wait_q, timeout);
+		result = z_pend_curr(&slab->lock, key, &slab->wait_q, timeout);
 		if (result == 0) {
 			*mem = _current->base.swap_data;
 		}
 		return result;
 	}
 
-	k_spin_unlock(&lock, key);
+	k_spin_unlock(&slab->lock, key);
 
 	return result;
 }
 
 void k_mem_slab_free(struct k_mem_slab *slab, void **mem)
 {
-	k_spinlock_key_t key = k_spin_lock(&lock);
+	k_spinlock_key_t key = k_spin_lock(&slab->lock);
 
 	if (slab->free_list == NULL) {
 		struct k_thread *pending_thread = z_unpend_first_thread(&slab->wait_q);
@@ -150,12 +149,12 @@ void k_mem_slab_free(struct k_mem_slab *slab, void **mem)
 		if (pending_thread != NULL) {
 			z_thread_return_value_set_with_data(pending_thread, 0, *mem);
 			z_ready_thread(pending_thread);
-			z_reschedule(&lock, key);
+			z_reschedule(&slab->lock, key);
 			return;
 		}
 	}
 	**(char ***) mem = slab->free_list;
 	slab->free_list = *(char **) mem;
 	slab->num_used--;
-	k_spin_unlock(&lock, key);
+	k_spin_unlock(&slab->lock, key);
 }