On 05/19/2014 03:13 PM, Maarten Lankhorst wrote:

op 19-05-14 15:42, Thomas Hellstrom schreef:

quoted

Hi, Maarten!

Some nitpicks, and that krealloc within rcu lock still worries me.
Otherwise looks good.

/Thomas



On 04/23/2014 12:15 PM, Maarten Lankhorst wrote:

quoted

@@ -55,8 +60,8 @@ int reservation_object_reserve_shared(struct

reservation_object *obj)
              kfree(obj->staged);
              obj->staged = NULL;
              return 0;
-        }
-        max = old->shared_max * 2;
+        } else
+            max = old->shared_max * 2;

Perhaps as a separate reformatting patch?

I'll fold it in to the patch that added
reservation_object_reserve_shared.

quoted

quoted

+
+int reservation_object_get_fences_rcu(struct reservation_object *obj,
+                      struct fence **pfence_excl,
+                      unsigned *pshared_count,
+                      struct fence ***pshared)
+{
+    unsigned shared_count = 0;
+    unsigned retry = 1;
+    struct fence **shared = NULL, *fence_excl = NULL;
+    int ret = 0;
+
+    while (retry) {
+        struct reservation_object_list *fobj;
+        unsigned seq;
+
+        seq = read_seqcount_begin(&obj->seq);
+
+        rcu_read_lock();
+
+        fobj = rcu_dereference(obj->fence);
+        if (fobj) {
+            struct fence **nshared;
+
+            shared_count = ACCESS_ONCE(fobj->shared_count);

ACCESS_ONCE() shouldn't be needed inside the seqlock?

Yes it is, shared_count may be increased, leading to potential
different sizes for krealloc and memcpy
if the ACCESS_ONCE is removed. I could use shared_max here instead,
which stays the same,
but it would waste more memory.

OK.

quoted

quoted

+            nshared = krealloc(shared, sizeof(*shared) *
shared_count, GFP_KERNEL);

Again, krealloc should be a sleeping function, and not suitable within a
RCU read lock? I still think this krealloc should be moved to the start
of the retry loop, and we should start with a suitable guess of
shared_count (perhaps 0?) It's not like we're going to waste a lot of
memory....

But shared_count is only known when holding the rcu lock.

What about this change?

Sure. That should work.

/Thomas