Add kmutex.c

1 files changed, 119 insertions, 0 deletions

diff --git a/kernel/proc/kmutex.c b/kernel/proc/kmutex.c
new file mode 100644
index 0000000..7e39d63
--- /dev/null
+++ b/kernel/proc/kmutex.c
@@ -0,0 +1,119 @@
+// SMP.1 + SMP.3
+// spinlock + mask interrupts
+#include "proc/kmutex.h"
+#include "globals.h"
+#include "main/interrupt.h"
+#include <errno.h>
+
+/*
+ * IMPORTANT: Mutexes can _NEVER_ be locked or unlocked from an
+ * interrupt context. Mutexes are _ONLY_ lock or unlocked from a
+ * thread context.
+ */
+
+/*
+ * Checks for the specific deadlock case where:
+ *  curthr wants mtx, but the owner of mtx is waiting on a mutex that curthr is
+ * holding
+ */
+#define DEBUG_DEADLOCKS 1
+void detect_deadlocks(kmutex_t *mtx)
+{
+#if DEBUG_DEADLOCKS
+    list_iterate(&curthr->kt_mutexes, held, kmutex_t, km_link)
+    {
+        list_iterate(&held->km_waitq.tq_list, waiter, kthread_t, kt_qlink)
+        {
+            if (waiter == mtx->km_holder)
+            {
+                panic(
+                    "detected deadlock between P%d and P%d (mutexes 0x%p, "
+                    "0x%p)\n",
+                    curproc->p_pid, waiter->kt_proc->p_pid, held, mtx);
+            }
+        }
+    }
+#endif
+}
+
+/*
+ * Initializes the members of mtx
+ */
+void kmutex_init(kmutex_t *mtx)
+{
+    /* PROCS {{{ */
+    mtx->km_holder = NULL;
+    sched_queue_init(&mtx->km_waitq);
+    list_link_init(&mtx->km_link);
+    /* PROCS }}} */
+}
+
+/*
+ * Obtains a mutex, potentially blocking.
+ *
+ * Hints:
+ * You are strongly advised to maintain the kt_mutexes member of curthr and call
+ * detect_deadlocks() to help debugging.
+ */
+void kmutex_lock(kmutex_t *mtx)
+{
+    /* PROCS {{{ */
+
+    dbg(DBG_ERROR, "locked mutex: %p\n", mtx);
+    KASSERT(curthr && "need thread context to lock mutex");
+    KASSERT(!kmutex_owns_mutex(mtx) && "already owner");
+
+    if (mtx->km_holder)
+    {
+        detect_deadlocks(mtx);
+        sched_sleep_on(&mtx->km_waitq);
+        KASSERT(kmutex_owns_mutex(mtx));
+    }
+    else
+    {
+        mtx->km_holder = curthr;
+        list_insert_tail(&curthr->kt_mutexes, &mtx->km_link);
+    }
+    /* PROCS }}} */
+}
+
+/*
+ * Releases a mutex.
+ *
+ * Hints:
+ * Again, you are strongly advised to maintain kt_mutexes.
+ * Use sched_wakeup_on() to hand off the mutex - think carefully about how
+ *  these two functions interact to ensure that the mutex's km_holder is
+ * properly set before the new owner is runnable.
+ */
+void kmutex_unlock(kmutex_t *mtx)
+{
+    /* PROCS {{{ */
+    dbg(DBG_ERROR, "unlocked mutex: %p\n", mtx);
+    KASSERT(curthr && (curthr == mtx->km_holder) &&
+            "unlocking a mutex we don\'t own");
+    sched_wakeup_on(&mtx->km_waitq, &mtx->km_holder);
+    KASSERT(!kmutex_owns_mutex(mtx));
+    list_remove(&mtx->km_link);
+    if (mtx->km_holder)
+        list_insert_tail(&mtx->km_holder->kt_mutexes, &mtx->km_link);
+
+    /* PROCS }}} */
+}
+
+/*
+ * Checks if mtx's wait queue is empty.
+ */
+long kmutex_has_waiters(kmutex_t *mtx)
+{
+    return !sched_queue_empty(&mtx->km_waitq);
+    ;
+}
+
+/*
+ * Checks if the current thread owns mtx.
+ */
+inline long kmutex_owns_mutex(kmutex_t *mtx)
+{
+    return curthr && mtx->km_holder == curthr;
+}