Changeset 31d8e10 in mainline for kernel/generic/src/mm/as.c

Timestamp:

2007-04-05T16:09:49Z (18 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

547fa39

Parents:

879585a3

Message:

Continue to de-oversynchronize the kernel.

• replace as→refcount with an atomic counter; accesses to this

reference counter are not to be done when the as→lock mutex is held;
this gets us rid of mutex_lock_active();

Remove the possibility of a deadlock between TLB shootdown and asidlock.

• get rid of mutex_lock_active() on as→lock
• when locking the asidlock spinlock, always do it conditionally and with

preemption disabled; in the unsuccessful case, enable interrupts and try again

• there should be no deadlock between TLB shootdown and the as→lock mutexes
• PLEASE REVIEW !!!

Add DEADLOCK_PROBE's to places where we have spinlock_trylock() loops.

File:

• kernel/generic/src/mm/as.c (modified) (10 diffs)

kernel/generic/src/mm/as.c

@@ -58 +58 @@
 #include <mm/asid.h>
 #include <arch/mm/asid.h>
+#include <preemption.h>
 #include <synch/spinlock.h>
 #include <synch/mutex.h>
@@ -182 +183 @@
                 as->asid = ASID_INVALID;
         
-        as->refcount = 0;
+        atomic_set(&as->refcount, 0);
         as->cpu_refcount = 0;
 #ifdef AS_PAGE_TABLE
@@ -197 +198 @@
  * 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)
@@ -202 +205 @@
         ipl_t ipl;
         bool cond;
-
-        ASSERT(as->refcount == 0);
+        DEADLOCK_PROBE_INIT(p_asidlock);
+
+        ASSERT(atomic_get(&as->refcount) == 0);
         
         /*
@@ -210 +214 @@
          */
 
-        ipl = interrupts_disable();
-        spinlock_lock(&asidlock);
+        /*
+         * 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_read();
+retry:
+        interrupts_disable();
+        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)
@@ -473 +492 @@
                  * Finish TLB shootdown sequence.
                  */
+
                 tlb_invalidate_pages(as->asid, area->base + pages * PAGE_SIZE,
                     area->pages - pages);
+                /*
+                 * 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();
                 
-                /*
-                 * Invalidate software translation caches (e.g. TSB on sparc64).
-                 */
-                as_invalidate_translation_cache(as, area->base +
-                    pages * PAGE_SIZE, area->pages - pages);
         } else {
                 /*
@@ -569 +589 @@
          * 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
@@ -577 +596 @@
          */
         as_invalidate_translation_cache(as, area->base, area->pages);
+        tlb_shootdown_finalize();
         
         btree_destroy(&area->used_space);
@@ -868 +888 @@
  * 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.
@@ -873 +895 @@
 void as_switch(as_t *old_as, as_t *new_as)
 {
-        spinlock_lock(&asidlock);
+        DEADLOCK_PROBE_INIT(p_asidlock);
+        preemption_disable();
+retry:
+        (void) interrupts_disable();
+        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();
 
         /*