Fix proc_kill () race, improve scheduler locking

kernel/proc/proc.c

@@ -153,6 +153,7 @@ static struct proc* proc_spawn_rd (char* name) {
   proc->pdata.regs.cs = 0x18 | 0x03;
   proc->pdata.regs.rip = aux.entry;
   proc->lock = SPIN_LOCK_INIT;
+  atomic_store (&proc->state, PROC_READY);
 #endif
 
   return proc;
@@ -181,26 +182,51 @@ static void proc_register (struct proc* proc) {
   spin_unlock (&procs_lock);
 }
 
+static struct proc *proc_find_sched (void) {
+  struct proc *start = thiscpu->proc_current;
+  struct proc *proc = start->next;
+
+  for (;;) {
+    if (proc == NULL) {
+      proc = thiscpu->proc_run_q;
+    }
+
+    if (atomic_load (&proc->state) == PROC_READY) {
+      return proc;
+    }
+
+    /* No runnable processes found. */
+    if (proc == start) {
+      return NULL;
+    }
+
+    proc = proc->next;
+  }
+}
+
 void proc_sched (void) {
+  struct proc *next = NULL;
+
   spin_lock (&thiscpu->lock);
 
   if (thiscpu->proc_run_q == NULL || thiscpu->proc_current == NULL) {
-    goto done;
+    spin_unlock (&thiscpu->lock);
+    goto idle;
   }
 
-  thiscpu->proc_current = thiscpu->proc_current->next;
+  next = proc_find_sched ();
 
-  if (thiscpu->proc_current == NULL) {
+  if (next != NULL) {
-    thiscpu->proc_current = thiscpu->proc_run_q;
+    thiscpu->proc_current = next;
   }
 
-done:
   spin_unlock (&thiscpu->lock);
 
-  if (thiscpu->proc_current != NULL) {
+  if (next != NULL && atomic_load (&next->state) == PROC_READY) {
-    do_sched (&thiscpu->proc_current->pdata.regs, &thiscpu->proc_current->pd);
+    do_sched (&next->pdata.regs, &next->pd);
   }
 
+idle:
 #if defined(__x86_64__)
   extern void amd64_spin (void);
 
@@ -209,23 +235,8 @@ done:
 }
 
 void proc_kill (struct proc* proc) {
-  spin_lock (&procs_lock);
+  /* mark for garbage collection */
-
+  atomic_store (&proc->state, PROC_DEAD);
-  spin_lock (&thiscpu->lock);
-
-  linklist_remove (struct procw*, procs, proc->procw);
-  linklist_remove (struct proc*, thiscpu->proc_run_q, proc);
-
-  if (thiscpu->proc_current == proc)
-    thiscpu->proc_current = NULL;
-
-  spin_unlock (&thiscpu->lock);
-
-  spin_unlock (&procs_lock);
-
-  /* clean up */
-  free (proc->procw);
-  free (proc);
 }
 
 static void proc_irq_sched (void* arg, void* regs) {

kernel/proc/proc.h

@@ -11,6 +11,12 @@
 #include <amd64/proc.h> /* USTACK_SIZE */
 #endif
 
+/// Process is ready to run
+#define PROC_READY  0
+/// Process marked garbage collection
+#define PROC_DEAD   1
+
+
 struct cpu;
 
 struct proc_mapping {
@@ -30,6 +36,7 @@ struct proc {
   spin_lock_t lock;
   struct cpu* cpu;
   struct procw* procw; /* link to it's global struct */
+  atomic_int state;
 };
 
 /*