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authorVitaly Kuznetsov <vkuznets@redhat.com>2015-03-27 19:10:13 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-04-03 17:18:02 +0300
commit0a1a86ac046091d7228c9f3a283dea5be96275dd (patch)
treecf4eca600c160ec8a00cbdd4f24794e246e0d822 /drivers/hv/hv_balloon.c
parent7fb0e1a65075a871c58cbcf8c877d1f9ae5cd83c (diff)
downloadlinux-0a1a86ac046091d7228c9f3a283dea5be96275dd.tar.xz
Drivers: hv: hv_balloon: survive ballooning request with num_pages=0
... and simplify alloc_balloon_pages() interface by removing redundant alloc_error from it. If we happen to enter balloon_up() with balloon_wrk.num_pages = 0 we will enter infinite 'while (!done)' loop as alloc_balloon_pages() will be always returning 0 and not setting alloc_error. We will also be sending a meaningless message to the host on every iteration. The 'alloc_unit == 1 && alloc_error -> num_ballooned == 0' change and alloc_error elimination requires a special comment. We do alloc_balloon_pages() with 2 different alloc_unit values and there are 4 different alloc_balloon_pages() results, let's check them all. alloc_unit = 512: 1) num_ballooned = 0, alloc_error = 0: we do 'alloc_unit=1' and retry pre- and post-patch. 2) num_ballooned > 0, alloc_error = 0: we check 'num_ballooned == num_pages' and act accordingly, pre- and post-patch. 3) num_ballooned > 0, alloc_error > 0: we report this chunk and remain within the loop, no changes here. 4) num_ballooned = 0, alloc_error > 0: we do 'alloc_unit=1' and retry pre- and post-patch. alloc_unit = 1: 1) num_ballooned = 0, alloc_error = 0: this can happen in two cases: when we passed 'num_pages=0' to alloc_balloon_pages() or when there was no space in bl_resp to place a single response. The second option is not possible as bl_resp is of PAGE_SIZE size and single response 'union dm_mem_page_range' is 8 bytes, but the first one is (in theory, I think that Hyper-V host never places such requests). Pre-patch code loops forever, post-patch code sends a reply with more_pages = 0 and finishes. 2) num_ballooned > 0, alloc_error = 0: we ran out of space in bl_resp, we report partial success and remain within the loop, no changes pre- and post-patch. 3) num_ballooned > 0, alloc_error > 0: pre-patch code finishes, post-patch code does one more try and if there is no progress (we finish with 'num_ballooned = 0') we finish. So we try a bit harder with this patch. 4) num_ballooned = 0, alloc_error > 0: both pre- and post-patch code enter 'more_pages = 0' branch and finish. So this patch has two real effects: 1) We reply with an empty response to 'num_pages=0' request. 2) We try a bit harder on alloc_unit=1 allocations (and reply with an empty tail reply in case we fail). An empty reply should be supported by host as we were able to send it even with pre-patch code when we were not able to allocate a single page. Suggested-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/hv/hv_balloon.c')
-rw-r--r--drivers/hv/hv_balloon.c19
1 files changed, 6 insertions, 13 deletions
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 4f5323cedab3..74312c88534a 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1081,9 +1081,9 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
-static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages,
- struct dm_balloon_response *bl_resp, int alloc_unit,
- bool *alloc_error)
+static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages,
+ struct dm_balloon_response *bl_resp,
+ int alloc_unit)
{
int i = 0;
struct page *pg;
@@ -1104,11 +1104,8 @@ static int alloc_balloon_pages(struct hv_dynmem_device *dm, int num_pages,
__GFP_NOMEMALLOC | __GFP_NOWARN,
get_order(alloc_unit << PAGE_SHIFT));
- if (!pg) {
- *alloc_error = true;
+ if (!pg)
return i * alloc_unit;
- }
-
dm->num_pages_ballooned += alloc_unit;
@@ -1140,7 +1137,6 @@ static void balloon_up(struct work_struct *dummy)
struct dm_balloon_response *bl_resp;
int alloc_unit;
int ret;
- bool alloc_error;
bool done = false;
int i;
struct sysinfo val;
@@ -1173,18 +1169,15 @@ 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);
+ bl_resp, alloc_unit);
if (alloc_unit != 1 && num_ballooned == 0) {
alloc_unit = 1;
continue;
}
- if ((alloc_unit == 1 && alloc_error) ||
- (num_ballooned == num_pages)) {
+ if (num_ballooned == 0 || num_ballooned == num_pages) {
bl_resp->more_pages = 0;
done = true;
dm_device.state = DM_INITIALIZED;