Fix scheduler starvation, use lists for scheduling

init/init.c

@@ -6,7 +6,7 @@
 #include <stdint.h>
 #include <string/string.h>
 
-#define EXAMPLE 1
+#define EXAMPLE 2
 
 #if EXAMPLE == 1
 
@@ -26,4 +26,46 @@ int spawn (void (*fn) (void)) {
 }
 
 void app_main (void) { spawn (&app_thread1); }
+#elif EXAMPLE == 2
+
+#define MUTEX 2000
+
+void app_thread1 (void);
+
+int spawn (void (*fn) (void)) {
+  size_t stack_size = 256 * PAGE_SIZE;
+  void* stack = malloc (stack_size);
+  if (stack == NULL)
+    return -ST_OOM_ERROR;
+
+  uintptr_t stack_top = (uintptr_t)stack + stack_size;
+  return clone (stack_top, stack_size, fn);
+}
+
+void app_main (void) {
+  create_mutex (MUTEX, RV_PRIVATE);
+
+  spawn (&app_thread1);
+
+  for (;;) {
+    /* lock_mutex (MUTEX, RV_PRIVATE); */
+
+    for (int i = 0; i < 3; i++)
+      test ('a');
+
+    /* unlock_mutex (MUTEX, RV_PRIVATE); */
+  }
+}
+
+void app_thread1 (void) {
+  for (int i = 0; i < 3; i++)
+    test ('b');
+  for (;;) {
+    /* lock_mutex (MUTEX, RV_PRIVATE); */
+
+    /* unlock_mutex (MUTEX, RV_PRIVATE); */
+  }
+
+  quit ();
+}
 #endif

kernel/amd64/smp.h

@@ -27,7 +27,7 @@ struct cpu {
 
   spin_lock_t lock;
 
-  struct rb_node_link* proc_run_q;
+  struct list_node_link* proc_run_q;
   struct proc* proc_current;
 };
 

kernel/amd64/syscall.c

@@ -25,12 +25,8 @@ int amd64_syscall_dispatch (void* stack_ptr) {
 
   struct proc* caller = thiscpu->proc_current;
 
-  __asm__ volatile ("sti");
-
   int result = func (caller, regs, regs->rdi, regs->rsi, regs->rdx, regs->r10, regs->r8, regs->r9);
 
-  __asm__ volatile ("cli");
-
   return result;
 }
 

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;
 };
 

libmsl/m/system.c

@@ -13,6 +13,8 @@ int quit (void) { return do_syscall (SYS_QUIT, 0); }
 
 int test (char c) { return do_syscall (SYS_TEST, c); }
 
+int sched (void) { return do_syscall (SYS_SCHED, 0); }
+
 int map (int mem_rid, int vis, uintptr_t vaddr, uint32_t flags) {
   return do_syscall (SYS_MAP, mem_rid, vis, vaddr, flags);
 }

libmsl/m/system.h

@@ -19,6 +19,7 @@
 
 int quit (void);
 int test (char c);
+int sched (void);
 int map (int mem_rid, int vis, uintptr_t vaddr, uint32_t flags);
 int unmap (uintptr_t vaddr, size_t pages);
 int create_mem (int mem_rid, int vis, size_t pages);