WebSVN – HelenOS – Diff – //branches/rcu/kernel/generic/src/mm/as.c

 #include <arch/mm/page.h>
 #include <genarch/mm/page_pt.h>
 #include <genarch/mm/page_ht.h>
 #include <mm/asid.h>
 #include <arch/mm/asid.h>
+#include <preemption.h>
 #include <synch/spinlock.h>
 #include <synch/mutex.h>
 #include <adt/list.h>
 #include <adt/btree.h>
 #include <proc/task.h>
     if (flags & FLAG_AS_KERNEL)
         as->asid = ASID_KERNEL;
     else
         as->asid = ASID_INVALID;
-    as->refcount = 0;
+    atomic_set(&as->refcount, 0);
     as->cpu_refcount = 0;
 #ifdef AS_PAGE_TABLE
     as->genarch.page_table = page_table_create(flags);
 #else
     page_table_create(flags);
 /** Destroy adress space.
+ *
  * When there are no tasks referencing this address space (i.e. its refcount is
  * zero), the address space can be destroyed.
+ *
+ * We know that we don't hold any spinlock.
  */
 void as_destroy(as_t *as)
+{
     ipl_t ipl;
     bool cond;
+    DEADLOCK_PROBE_INIT(p_asidlock);
-    ASSERT(as->refcount == 0);
+    ASSERT(atomic_get(&as->refcount) == 0);
     /*
      * Since there is no reference to this area,
      * it is safe not to lock its mutex.
      */
+    /*
+     * We need to avoid deadlock between TLB shootdown and asidlock.
+     * We therefore try to take asid conditionally and if we don't succeed,
+     * we enable interrupts and try again. This is done while preemption is
+     * disabled to prevent nested context switches. We also depend on the
+     * fact that so far no spinlocks are held.
+     */
+    preemption_disable();
-    ipl = interrupts_disable();
+    ipl = interrupts_read();
+retry:
+    interrupts_disable();
-    spinlock_lock(&asidlock);
+    if (!spinlock_trylock(&asidlock)) {
+        interrupts_enable();
+        DEADLOCK_PROBE(p_asidlock, DEADLOCK_THRESHOLD);
+        goto retry;
+    }
+    preemption_enable();    /* Interrupts disabled, enable preemption */
     if (as->asid != ASID_INVALID && as != AS_KERNEL) {
         if (as != AS && as->cpu_refcount == 0)
             list_remove(&as->inactive_as_with_asid_link);
         asid_put(as->asid);
+    }
+        }
         /*
          * Finish TLB shootdown sequence.
          */
         tlb_invalidate_pages(as->asid, area->base + pages * PAGE_SIZE,
             area->pages - pages);
-        tlb_shootdown_finalize();
         /*
          * Invalidate software translation caches (e.g. TSB on sparc64).
          */
         as_invalidate_translation_cache(as, area->base +
             pages * PAGE_SIZE, area->pages - pages);
+        tlb_shootdown_finalize();
     } else {
         /*
          * Growing the area.
          * Check for overlaps with other address space areas.
          */
+    }
     /*
      * Finish TLB shootdown sequence.
      */
     tlb_invalidate_pages(as->asid, area->base, area->pages);
-    tlb_shootdown_finalize();
     /*
      * Invalidate potential software translation caches (e.g. TSB on
      * sparc64).
      */
     as_invalidate_translation_cache(as, area->base, area->pages);
+    tlb_shootdown_finalize();
     btree_destroy(&area->used_space);
     area->attributes |= AS_AREA_ATTR_PARTIAL;
+ *
  * Note that this function cannot sleep as it is essentially a part of
  * scheduling. Sleeping here would lead to deadlock on wakeup. Another
  * thing which is forbidden in this context is locking the address space.
+ *
+ * When this function is enetered, no spinlocks may be held.
+ *
  * @param old Old address space or NULL.
  * @param new New address space.
  */
 void as_switch(as_t *old_as, as_t *new_as)
+{
+    DEADLOCK_PROBE_INIT(p_asidlock);
+    preemption_disable();
+retry:
+    (void) interrupts_disable();
-    spinlock_lock(&asidlock);
+    if (!spinlock_trylock(&asidlock)) {
+        /*
+         * Avoid deadlock with TLB shootdown.
+         * We can enable interrupts here because
+         * preemption is disabled. We should not be
+         * holding any other lock.
+         */
+        (void) interrupts_enable();
+        DEADLOCK_PROBE(p_asidlock, DEADLOCK_THRESHOLD);
+        goto retry;
+    }
+    preemption_enable();
     /*
      * First, take care of the old address space.
      */
     if (old_as) {

Subversion Repositories HelenOS

(root)//branches/rcu/kernel/generic/src/mm/as.c – Rev 2292 → 2307