IB/hfi1: Make use of mm consistent

The hfi1 driver registers a mmu_notifier callback when /dev/hfi1_* is
opened, and unregisters it when the device is closed.  The driver
incorrectly assumes that the close will always happen from the same
context as the open.  In particular, closes due to SIGKILL or OOM killer
activity may happen from a different context.  In these cases, the wrong
mm is passed to mmu_notifier_unregister(), which causes improper reference
counting for the victim mm, and eventual memory corruption.

Preserve the mm for all open file descriptors and use this mm rather than
current->mm for memory operations for the lifetime of that fd.  Note: this
patch leaves 1 use of current->mm in place.  This use is removed in a
follow on patch because other functional changes were required prior to
that use being removed.

If registration fails, there is no reason to keep the handler object
around.  Free the handler object rather than add it to the list to
prevent any mmu_notifier operations, including unregister, when
registration fails.

Suggested-by: Jim Foraker <foraker1@llnl.gov>
Reviewed-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/hfi1/mmu_rb.c

@@ -58,6 +58,7 @@ struct mmu_rb_handler {
 	struct rb_root *root;
 	spinlock_t lock;        /* protect the RB tree */
 	struct mmu_rb_ops *ops;
+	struct mm_struct *mm;
 };
 
 static LIST_HEAD(mmu_rb_handlers);
@@ -95,9 +96,11 @@ static unsigned long mmu_node_last(struct mmu_rb_node *node)
 	return PAGE_ALIGN(node->addr + node->len) - 1;
 }
 
-int hfi1_mmu_rb_register(struct rb_root *root, struct mmu_rb_ops *ops)
+int hfi1_mmu_rb_register(struct mm_struct *mm, struct rb_root *root,
+			 struct mmu_rb_ops *ops)
 {
 	struct mmu_rb_handler *handlr;
+	int ret;
 
 	handlr = kmalloc(sizeof(*handlr), GFP_KERNEL);
 	if (!handlr)
@@ -108,11 +111,19 @@ int hfi1_mmu_rb_register(struct rb_root *root, struct mmu_rb_ops *ops)
 	INIT_HLIST_NODE(&handlr->mn.hlist);
 	spin_lock_init(&handlr->lock);
 	handlr->mn.ops = &mn_opts;
+	handlr->mm = mm;
+
+	ret = mmu_notifier_register(&handlr->mn, handlr->mm);
+	if (ret) {
+		kfree(handlr);
+		return ret;
+	}
+
 	spin_lock(&mmu_rb_lock);
 	list_add_tail_rcu(&handlr->list, &mmu_rb_handlers);
 	spin_unlock(&mmu_rb_lock);
 
-	return mmu_notifier_register(&handlr->mn, current->mm);
+	return ret;
 }
 
 void hfi1_mmu_rb_unregister(struct rb_root *root)
@@ -126,8 +137,7 @@ void hfi1_mmu_rb_unregister(struct rb_root *root)
 		return;
 
 	/* Unregister first so we don't get any more notifications. */
-	if (current->mm)
-		mmu_notifier_unregister(&handler->mn, current->mm);
+	mmu_notifier_unregister(&handler->mn, handler->mm);
 
 	spin_lock(&mmu_rb_lock);
 	list_del_rcu(&handler->list);