From 45f420a338ea02225bb8a98c9aca5eed8d6a23ae Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Sun, 2 Jun 2024 00:26:57 +0200
Subject: Initial commit

---
 kernel/spinlock.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 kernel/spinlock.c

(limited to 'kernel/spinlock.c')

diff --git a/kernel/spinlock.c b/kernel/spinlock.c
new file mode 100644
index 0000000..8f9c654
--- /dev/null
+++ b/kernel/spinlock.c
@@ -0,0 +1,77 @@
+#include "kernel/spinlock.h"
+#include "kernel/cpu.h"
+#include "kernel/riscv.h"
+#include "kernel/atomic.h"
+
+#define NO_CPU 0xffff'ffff
+
+static bool current_cpu_holding(const Spinlock* lock)
+{
+    return lock->locking == current_cpu()->id;
+}
+
+static void push_intr_off()
+{
+    Cpu* cpu = current_cpu();
+    
+    bool old_intr_enabled = (rc_sstatus(SSTATUS_SIE) & SSTATUS_SIE) != 0;
+    if (cpu->intr_off_count == 0)
+    {
+        cpu->intr_enabled_before_off = old_intr_enabled;
+    }
+
+    cpu->intr_off_count += 1;
+}
+
+static void pop_intr_off()
+{
+    Cpu* cpu = current_cpu();
+
+    if (cpu->intr_off_count == 0)
+    {
+        panic("pop_intr_off: count = 0");
+    }
+
+    cpu->intr_off_count -= 1;
+    if (cpu->intr_off_count == 0 && cpu->intr_enabled_before_off)
+    {
+        s_sstatus(SSTATUS_SIE);
+    }
+}
+
+void spinlock_init(Spinlock* lock)
+{
+    lock->next_ticket = 0;
+    lock->serving = 0;
+    lock->locking = NO_CPU;
+}
+
+void spinlock_acquire(Spinlock* lock)
+{
+    if (current_cpu_holding(lock))
+    {
+        panic("spinlock_acquire: already held");
+    }
+
+    push_intr_off();
+    
+    uint32_t ticket = atomic_fetch_add(&lock->next_ticket, 1, MEM_RELAXED);
+
+    while (atomic_load(&lock->serving, MEM_RELAXED) != ticket) {}
+    atomic_fence(MEM_ACQUIRE);
+
+    lock->locking = current_cpu()->id;
+}
+
+void spinlock_release(Spinlock* lock)
+{
+    if (!current_cpu_holding(lock))
+    {
+        panic("spinlock_release: not held");
+    }
+
+    lock->locking = NO_CPU;
+    atomic_fetch_add(&lock->serving, 1, MEM_RELEASE);
+    
+    pop_intr_off();
+}
-- 
cgit