Changeset 481d4751 in mainline

Timestamp:

2010-05-02T18:52:45Z (15 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

1624aae

Parents:

663bb537

Message:

Fix a race condition between the scheduler and as_destroy().

It was possible for the scheduler to use page tables of an address space which
was already destroyed. Prevent this from happening by holding extra references
to the current task and the current address space in
scheduler_separated_stack().

File:

• kernel/generic/src/proc/scheduler.c (modified) (4 diffs)

kernel/generic/src/proc/scheduler.c

@@ -1 +1 @@
 /*
- * Copyright (c) 2001-2007 Jakub Jermar
+ * Copyright (c) 2010 Jakub Jermar
  * All rights reserved.
  *
@@ -382 +382 @@
         int priority;
         DEADLOCK_PROBE_INIT(p_joinwq);
+        task_t *old_task = TASK;
+        as_t *old_as = AS;
 
         ASSERT(CPU != NULL);
         
+        /*
+         * Hold the current task and the address space to prevent their
+         * possible destruction should thread_destroy() be called on this or any
+         * other processor while the scheduler is still using them.
+         */
+        if (old_task)
+                task_hold(old_task);
+        if (old_as)
+                as_hold(old_as);
+
         if (THREAD) {
                 /* must be run after the switch to scheduler stack */
@@ -476 +488 @@
          */
         if (TASK != THREAD->task) {
-                as_t *as1 = NULL;
-                as_t *as2;
-
-                if (TASK) {
-                        spinlock_lock(&TASK->lock);
-                        as1 = TASK->as;
-                        spinlock_unlock(&TASK->lock);
-                }
-
-                spinlock_lock(&THREAD->task->lock);
-                as2 = THREAD->task->as;
-                spinlock_unlock(&THREAD->task->lock);
+                as_t *new_as = THREAD->task->as;
                 
                 /*
@@ -493 +494 @@
                  * space.
                  */
-                if (as1 != as2) {
+                if (old_as != new_as) {
                         /*
                          * Both tasks and address spaces are different.
                          * Replace the old one with the new one.
                          */
-                        as_switch(as1, as2);
+                        as_switch(old_as, new_as);
                 }
+
                 TASK = THREAD->task;
                 before_task_runs();
         }
 
+        if (old_task)
+                task_release(old_task);
+        if (old_as)
+                as_release(old_as);
+        
         spinlock_lock(&THREAD->lock);   
         THREAD->state = Running;