[PATCH v2] hv: hv_balloon: avoid memory leak on alloc_error of 2MB memory block

[Dexuan Cui <decui@microsoft.com>]

If num_ballooned is not 0, we shouldn't neglect the
already-partially-allocated 2MB memory block(s).

Cc: Jason Wang <jasowang@redhat.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---

v2: I fixed the logic error in v1, pointed by Jason Wang:
	In v1: in the case of partially-allocated 2MB, alloc_error is true,
	so we'll run "done = true" and hence we won't proceed with
	the next iteration of trying 4K allocation.

    I also changed the WARN_ON to WARN_ON_ONCE in case the host behavior
    changes in the future.

 drivers/hv/hv_balloon.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 5e90c5d..b958ded 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1087,10 +1087,12 @@ static void balloon_up(struct work_struct *dummy)
 	struct dm_balloon_response *bl_resp;
 	int alloc_unit;
 	int ret;
-	bool alloc_error = false;
+	bool alloc_error;
 	bool done = false;
 	int i;
 
+	/* The host balloons pages in 2M granularity. */
+	WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0);
 
 	/*
 	 * We will attempt 2M allocations. However, if we fail to
@@ -1107,16 +1109,18 @@ static void balloon_up(struct work_struct *dummy)
 
 
 		num_pages -= num_ballooned;
+		alloc_error = false;
 		num_ballooned = alloc_balloon_pages(&dm_device, num_pages,
 						bl_resp, alloc_unit,
 						 &alloc_error);
 
-		if ((alloc_error) && (alloc_unit != 1)) {
+		if (alloc_unit != 1 && num_ballooned == 0) {
 			alloc_unit = 1;
 			continue;
 		}
 
-		if ((alloc_error) || (num_ballooned == num_pages)) {
+		if ((alloc_unit == 1 && alloc_error) ||
+			(num_ballooned == num_pages)) {
 			bl_resp->more_pages = 0;
 			done = true;
 			dm_device.state = DM_INITIALIZED;
-- 
1.9.1