Use RW spin locks

kernel/sync/rw_spin_lock.c

@@ -0,0 +1,59 @@
+#include <libk/assert.h>
+#include <libk/std.h>
+#include <sync/rw_spin_lock.h>
+#include <sys/debug.h>
+#include <sys/spin_lock.h>
+
+#define WRITER_WAIT (1U << 31)
+#define READER_MASK (~WRITER_WAIT)
+
+void rw_spin_read_lock (rw_spin_lock_t* rw) {
+  uint32_t value;
+
+  for (;;) {
+    value = atomic_load_explicit (rw, memory_order_relaxed);
+
+    if ((value & WRITER_WAIT) == 0) {
+      if (atomic_compare_exchange_weak_explicit (rw, &value, value + 1, memory_order_acquire,
+                                                 memory_order_relaxed)) {
+        return;
+      }
+    }
+
+    spin_lock_relax ();
+  }
+}
+
+void rw_spin_read_unlock (rw_spin_lock_t* rw) {
+  uint32_t old = atomic_fetch_sub_explicit (rw, 1, memory_order_release);
+  assert ((old & READER_MASK) > 0);
+}
+
+void rw_spin_write_lock (rw_spin_lock_t* rw) {
+  uint32_t value;
+
+  /* announce writer */
+  for (;;) {
+    value = atomic_load_explicit (rw, memory_order_relaxed);
+
+    if ((value & WRITER_WAIT) == 0) {
+      if (atomic_compare_exchange_weak_explicit (rw, &value, (value | WRITER_WAIT),
+                                                 memory_order_acquire, memory_order_relaxed))
+        break;
+    } else
+      spin_lock_relax ();
+  }
+
+  /* wait for readers */
+  for (;;) {
+    value = atomic_load_explicit (rw, memory_order_acquire);
+    if ((value & READER_MASK) == 0)
+      return;
+
+    spin_lock_relax ();
+  }
+}
+
+void rw_spin_write_unlock (rw_spin_lock_t* rw) {
+  atomic_store_explicit (rw, 0, memory_order_release);
+}