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Diffstat (limited to 'kernel/locking/osq_lock.c')
-rw-r--r--kernel/locking/osq_lock.c37
1 files changed, 20 insertions, 17 deletions
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index d5610ad52b..75a6f61338 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -11,6 +11,13 @@
* called from interrupt context and we have preemption disabled while
* spinning.
*/
+
+struct optimistic_spin_node {
+ struct optimistic_spin_node *next, *prev;
+ int locked; /* 1 if lock acquired */
+ int cpu; /* encoded CPU # + 1 value */
+};
+
static DEFINE_PER_CPU_SHARED_ALIGNED(struct optimistic_spin_node, osq_node);
/*
@@ -37,32 +44,28 @@ static inline struct optimistic_spin_node *decode_cpu(int encoded_cpu_val)
/*
* Get a stable @node->next pointer, either for unlock() or unqueue() purposes.
* Can return NULL in case we were the last queued and we updated @lock instead.
+ *
+ * If osq_lock() is being cancelled there must be a previous node
+ * and 'old_cpu' is its CPU #.
+ * For osq_unlock() there is never a previous node and old_cpu is
+ * set to OSQ_UNLOCKED_VAL.
*/
static inline struct optimistic_spin_node *
osq_wait_next(struct optimistic_spin_queue *lock,
struct optimistic_spin_node *node,
- struct optimistic_spin_node *prev)
+ int old_cpu)
{
- struct optimistic_spin_node *next = NULL;
int curr = encode_cpu(smp_processor_id());
- int old;
-
- /*
- * If there is a prev node in queue, then the 'old' value will be
- * the prev node's CPU #, else it's set to OSQ_UNLOCKED_VAL since if
- * we're currently last in queue, then the queue will then become empty.
- */
- old = prev ? prev->cpu : OSQ_UNLOCKED_VAL;
for (;;) {
if (atomic_read(&lock->tail) == curr &&
- atomic_cmpxchg_acquire(&lock->tail, curr, old) == curr) {
+ atomic_cmpxchg_acquire(&lock->tail, curr, old_cpu) == curr) {
/*
* We were the last queued, we moved @lock back. @prev
* will now observe @lock and will complete its
* unlock()/unqueue().
*/
- break;
+ return NULL;
}
/*
@@ -76,15 +79,15 @@ osq_wait_next(struct optimistic_spin_queue *lock,
* wait for a new @node->next from its Step-C.
*/
if (node->next) {
+ struct optimistic_spin_node *next;
+
next = xchg(&node->next, NULL);
if (next)
- break;
+ return next;
}
cpu_relax();
}
-
- return next;
}
bool osq_lock(struct optimistic_spin_queue *lock)
@@ -186,7 +189,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
* back to @prev.
*/
- next = osq_wait_next(lock, node, prev);
+ next = osq_wait_next(lock, node, prev->cpu);
if (!next)
return false;
@@ -226,7 +229,7 @@ void osq_unlock(struct optimistic_spin_queue *lock)
return;
}
- next = osq_wait_next(lock, node, NULL);
+ next = osq_wait_next(lock, node, OSQ_UNLOCKED_VAL);
if (next)
WRITE_ONCE(next->locked, 1);
}