vmware balloon: clamp number of collected non-balloonable pages

Limit number of accumulated non-balloonable pages during inflation cycle,
otherwise there is a chance we will be spinning and growing the list
forever.  This happens during torture tests when balloon target changes
while we are in the middle of inflation cycle and monitor starts refusing
to lock pages (since they are not needed anymore).
Signed-off-by: Dmitry Torokhov <dtor@vmware.com>
Acked-by: Bhavesh Davda <bhavesh@vmware.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/misc/vmware_balloon.c

@@ -45,7 +45,7 @@
 
 MODULE_AUTHOR("VMware, Inc.");
 MODULE_DESCRIPTION("VMware Memory Control (Balloon) Driver");
-MODULE_VERSION("1.2.1.0-K");
+MODULE_VERSION("1.2.1.1-k");
 MODULE_ALIAS("dmi:*:svnVMware*:*");
 MODULE_ALIAS("vmware_vmmemctl");
 MODULE_LICENSE("GPL");
@@ -101,6 +101,8 @@ MODULE_LICENSE("GPL");
 /* Maximum number of page allocations without yielding processor */
 #define VMW_BALLOON_YIELD_THRESHOLD	1024
 
+/* Maximum number of refused pages we accumulate during inflation cycle */
+#define VMW_BALLOON_MAX_REFUSED		16
 
 /*
  * Hypervisor communication port definitions.
@@ -183,6 +185,7 @@ struct vmballoon {
 
 	/* transient list of non-balloonable pages */
 	struct list_head refused_pages;
+	unsigned int n_refused_pages;
 
 	/* balloon size in pages */
 	unsigned int size;
@@ -428,14 +431,21 @@ static int vmballoon_reserve_page(struct vmballoon *b, bool can_sleep)
 		/* inform monitor */
 		locked = vmballoon_send_lock_page(b, page_to_pfn(page));
 		if (!locked) {
+			STATS_INC(b->stats.refused_alloc);
+
 			if (b->reset_required) {
 				__free_page(page);
 				return -EIO;
 			}
 
-			/* place on list of non-balloonable pages, retry allocation */
+			/*
+			 * Place page on the list of non-balloonable pages
+			 * and retry allocation, unless we already accumulated
+			 * too many of them, in which case take a breather.
+			 */
 			list_add(&page->lru, &b->refused_pages);
-			STATS_INC(b->stats.refused_alloc);
+			if (++b->n_refused_pages >= VMW_BALLOON_MAX_REFUSED)
+				return -EIO;
 		}
 	} while (!locked);
 
@@ -483,6 +493,8 @@ static void vmballoon_release_refused_pages(struct vmballoon *b)
 		__free_page(page);
 		STATS_INC(b->stats.refused_free);
 	}
+
+	b->n_refused_pages = 0;
 }
 
 /*