From 0a1a86ac046091d7228c9f3a283dea5be96275dd Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Fri, 27 Mar 2015 09:10:13 -0700 Subject: 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 Signed-off-by: Vitaly Kuznetsov Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman --- drivers/hv/hv_balloon.c | 19 ++++++------------- 1 file 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; -- cgit v1.2.2