Fix scheduler starvation, use lists for scheduling

kernel/proc/mutex.c

@@ -34,6 +34,7 @@ try:
 
   spin_unlock (&mutex->resource->lock, &ctxmt);
 
+  DEBUG ("proc->pid=%d\n", proc->pid);
   proc_suspend (proc, &mutex->suspension_q);
 
   goto try;
@@ -52,11 +53,10 @@ bool proc_mutex_unlock (struct proc* proc, struct proc_mutex* mutex) {
   spin_lock (&mutex->suspension_q.lock, &ctxsq);
 
   struct proc* resumed_proc = NULL;
-  struct rb_node_link* node;
-  rbtree_first (&mutex->suspension_q.proc_tree, node);
+  struct list_node_link* node = mutex->suspension_q.proc_list;
 
   if (node) {
-    resumed_proc = rbtree_entry (node, struct proc, suspension_link);
+    resumed_proc = list_entry (node, struct proc, suspension_link);
     mutex->owner = resumed_proc;
     mutex->locked = true;
 

kernel/proc/proc.c

@@ -28,14 +28,6 @@
 
 #define SCHED_REAP_FREQ 10
 
-/*
- * Lock hierachy:
- * - proc_tree_lock
- *   - cpu->lock
- *     - proc->lock
- *       - suspension_q->lock
- */
-
 static struct rb_node_link* proc_tree = NULL;
 static rw_spin_lock_t proc_tree_lock = RW_SPIN_LOCK_INIT;
 
@@ -217,49 +209,46 @@ void proc_register (struct proc* proc, struct cpu* cpu) {
 
   proc->cpu = cpu;
 
+  rw_spin_write_lock (&proc_tree_lock, &ctxprtr);
+  rbtree_insert (struct proc, &proc_tree, &proc->proc_tree_link, proc_tree_link, pid);
+  rw_spin_write_unlock (&proc_tree_lock, &ctxprtr);
+
   spin_lock (&cpu->lock, &ctxcpu);
-  rbtree_insert (struct proc, &cpu->proc_run_q, &proc->cpu_run_q_link, cpu_run_q_link, pid);
+  list_append (cpu->proc_run_q, &proc->cpu_run_q_link);
 
   if (cpu->proc_current == NULL)
     cpu->proc_current = proc;
 
   spin_unlock (&cpu->lock, &ctxcpu);
-
-  rw_spin_write_lock (&proc_tree_lock, &ctxprtr);
-  rbtree_insert (struct proc, &proc_tree, &proc->proc_tree_link, proc_tree_link, pid);
-  rw_spin_write_unlock (&proc_tree_lock, &ctxprtr);
 }
 
 /* caller holds cpu->lock */
 static struct proc* proc_find_sched (struct cpu* cpu) {
-  struct rb_node_link* node = NULL;
-  struct proc* current = cpu->proc_current;
-  struct proc* proc = NULL;
-
-  if (current)
-    rbtree_next (&current->cpu_run_q_link, node);
-
-  if (!node)
-    rbtree_first (&cpu->proc_run_q, node);
-
-  if (!node)
+  if (!cpu->proc_run_q)
     return NULL;
 
-  struct rb_node_link* first = node;
+  struct list_node_link *current, *start;
+
+  if (cpu->proc_current)
+    current = cpu->proc_current->cpu_run_q_link.next;
+  else
+    current = cpu->proc_run_q;
+
+  if (!current)
+    current = cpu->proc_run_q;
+
+  start = current;
+
   do {
-    proc = rbtree_entry (node, struct proc, cpu_run_q_link);
+    struct proc* proc = list_entry (current, struct proc, cpu_run_q_link);
 
     if (atomic_load (&proc->state) == PROC_READY)
       return proc;
 
-    rbtree_next (node, node);
+    current = current->next ? current->next : cpu->proc_run_q;
+  } while (current != start);
 
-    if (!node)
-      rbtree_first (&cpu->proc_run_q, node);
-
-  } while (node != first);
-
-  return ((atomic_load (&current->state) == PROC_READY) ? current : NULL);
+  return NULL;
 }
 
 static void proc_reap (void) {
@@ -281,9 +270,8 @@ static void proc_reap (void) {
     if (atomic_load (&proc->state) == PROC_DEAD) {
       spin_lock (&proc->lock, &ctxpr);
       rbtree_delete (&proc_tree, &proc->proc_tree_link);
-      spin_unlock (&proc->lock, &ctxpr);
-
       list_append (reap_list, &proc->reap_link);
+      spin_unlock (&proc->lock, &ctxpr);
     }
 
     node = next;
@@ -318,7 +306,7 @@ void proc_sched (void* regs) {
 
   if (prev != NULL) {
     spin_lock (&prev->lock, &ctxpr);
-    prev->pdata.regs = *(struct saved_regs*)regs;
+    memcpy (&prev->pdata.regs, regs, sizeof (struct saved_regs));
     spin_unlock (&prev->lock, &ctxpr);
   }
 
@@ -347,7 +335,7 @@ void proc_kill (struct proc* proc) {
 
   spin_lock (&cpu->lock, &ctxcpu);
 
-  rbtree_delete (&cpu->proc_run_q, &proc->cpu_run_q_link);
+  list_remove (cpu->proc_run_q, &proc->cpu_run_q_link);
   if (cpu->proc_current == proc)
     cpu->proc_current = NULL;
 
@@ -370,13 +358,13 @@ void proc_suspend (struct proc* proc, struct proc_suspension_q* sq) {
   /* remove from run q */
   spin_lock (&cpu->lock, &ctxcpu);
 
-  rbtree_delete (&cpu->proc_run_q, &proc->cpu_run_q_link);
+  list_remove (cpu->proc_run_q, &proc->cpu_run_q_link);
   if (cpu->proc_current == proc)
     cpu->proc_current = NULL;
   spin_unlock (&cpu->lock, &ctxcpu);
 
   spin_lock (&sq->lock, &ctxsq);
-  rbtree_insert (struct proc, &sq->proc_tree, &proc->suspension_link, suspension_link, pid);
+  list_append (sq->proc_list, &proc->suspension_link);
   spin_unlock (&sq->lock, &ctxsq);
 
   cpu_request_sched (cpu);
@@ -388,7 +376,7 @@ void proc_resume (struct proc* proc) {
   struct proc_suspension_q* sq = proc->suspension_q;
 
   spin_lock (&sq->lock, &ctxsq);
-  rbtree_delete (&sq->proc_tree, &proc->suspension_link);
+  list_remove (sq->proc_list, &proc->suspension_link);
   spin_unlock (&sq->lock, &ctxsq);
 
   spin_lock (&proc->lock, &ctxpr);
@@ -397,7 +385,7 @@ void proc_resume (struct proc* proc) {
   spin_unlock (&proc->lock, &ctxpr);
 
   spin_lock (&cpu->lock, &ctxcpu);
-  rbtree_insert (struct proc, &cpu->proc_run_q, &proc->cpu_run_q_link, cpu_run_q_link, pid);
+  list_append (cpu->proc_run_q, &proc->cpu_run_q_link);
   spin_unlock (&cpu->lock, &ctxcpu);
 
   cpu_request_sched (cpu);

kernel/proc/proc.h

@@ -45,8 +45,8 @@ struct proc_resources {
 struct proc {
   int pid;
   struct rb_node_link proc_tree_link;
-  struct rb_node_link cpu_run_q_link;
-  struct rb_node_link suspension_link;
+  struct list_node_link cpu_run_q_link;
+  struct list_node_link suspension_link;
   struct list_node_link reap_link;
 
   struct list_node_link* mappings; /* pd.lock implicitly protects this field */

kernel/proc/suspension_q.h

@@ -1,11 +1,11 @@
 #ifndef _KERNEL_PROC_SUSPENTION_Q_H
 #define _KERNEL_PROC_SUSPENTION_Q_H
 
-#include <libk/rbtree.h>
+#include <libk/list.h>
 #include <sync/spin_lock.h>
 
 struct proc_suspension_q {
-  struct rb_node_link* proc_tree;
+  struct list_node_link* proc_list;
   spin_lock_t lock;
 };