Changeset 879585a3 in mainline for kernel/generic/src/mm/as.c

Timestamp:

2007-03-31T22:22:50Z (18 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

31d8e10

Parents:

563c2dd

Message:

Simplify synchronization in as_switch().
The function was oversynchronized, which
was causing deadlocks on the address
space mutex.

Now, address spaces can only be switched
when the asidlock is held. This also protects
stealing of ASIDs. No other synchronization
is necessary.

File:

• kernel/generic/src/mm/as.c (modified) (9 diffs)

kernel/generic/src/mm/as.c

@@ -96 +96 @@
 
 /**
- * This lock protects inactive_as_with_asid_head list. It must be acquired
- * before as_t mutex.
- */
-SPINLOCK_INITIALIZE(inactive_as_with_asid_lock);
+ * This lock serializes access to the ASID subsystem.
+ * It protects:
+ * - inactive_as_with_asid_head list
+ * - as->asid for each as of the as_t type
+ * - asids_allocated counter
+ */
+SPINLOCK_INITIALIZE(asidlock);
 
 /**
@@ -206 +209 @@
          * it is safe not to lock its mutex.
          */
+
         ipl = interrupts_disable();
-        spinlock_lock(&inactive_as_with_asid_lock);
+        spinlock_lock(&asidlock);
         if (as->asid != ASID_INVALID && as != AS_KERNEL) {
                 if (as != AS && as->cpu_refcount == 0)
@@ -213 +217 @@
                 asid_put(as->asid);
         }
-        spinlock_unlock(&inactive_as_with_asid_lock);
+        spinlock_unlock(&asidlock);
 
         /*
@@ -861 +865 @@
  *
  * Note that this function cannot sleep as it is essentially a part of
- * scheduling. Sleeping here would lead to deadlock on wakeup.
+ * scheduling. Sleeping here would lead to deadlock on wakeup. Another
+ * thing which is forbidden in this context is locking the address space.
  *
  * @param old Old address space or NULL.
@@ -868 +873 @@
 void as_switch(as_t *old_as, as_t *new_as)
 {
-        ipl_t ipl;
-        bool needs_asid = false;
-        
-        ipl = interrupts_disable();
-        spinlock_lock(&inactive_as_with_asid_lock);
+        spinlock_lock(&asidlock);
 
         /*
@@ -878 +879 @@
          */     
         if (old_as) {
-                mutex_lock_active(&old_as->lock);
                 ASSERT(old_as->cpu_refcount);
                 if((--old_as->cpu_refcount == 0) && (old_as != AS_KERNEL)) {
@@ -891 +891 @@
                             &inactive_as_with_asid_head);
                 }
-                mutex_unlock(&old_as->lock);
 
                 /*
@@ -903 +902 @@
          * Second, prepare the new address space.
          */
-        mutex_lock_active(&new_as->lock);
         if ((new_as->cpu_refcount++ == 0) && (new_as != AS_KERNEL)) {
-                if (new_as->asid != ASID_INVALID) {
+                if (new_as->asid != ASID_INVALID)
                         list_remove(&new_as->inactive_as_with_asid_link);
-                } else {
-                        /*
-                         * Defer call to asid_get() until new_as->lock is released.
-                         */
-                        needs_asid = true;
-                }
+                else
+                        new_as->asid = asid_get();
         }
 #ifdef AS_PAGE_TABLE
         SET_PTL0_ADDRESS(new_as->genarch.page_table);
 #endif
-        mutex_unlock(&new_as->lock);
-
-        if (needs_asid) {
-                /*
-                 * Allocation of new ASID was deferred
-                 * until now in order to avoid deadlock.
-                 */
-                asid_t asid;
-                
-                asid = asid_get();
-                mutex_lock_active(&new_as->lock);
-                new_as->asid = asid;
-                mutex_unlock(&new_as->lock);
-        }
-        spinlock_unlock(&inactive_as_with_asid_lock);
-        interrupts_restore(ipl);
         
         /*
@@ -939 +917 @@
          */
         as_install_arch(new_as);
+
+        spinlock_unlock(&asidlock);
         
         AS = new_as;