[PATCH v3 1/4] xen/balloon: fix accounting in alloc_xenballooned_pages error path

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

target_unpopulated is incremented with nr_pages at the start of the
function, but the call to free_xenballooned_pages will only subtract
pgno number of pages, and thus the rest need to be subtracted before
returning or else accounting will be skewed.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
---
 drivers/xen/balloon.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 77c57568e5d7..3cb10ed32557 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -630,6 +630,12 @@ int alloc_xenballooned_pages(int nr_pages, struct page 
**pages)
  out_undo:
        mutex_unlock(&balloon_mutex);
        free_xenballooned_pages(pgno, pages);
+       /*
+        * NB: free_xenballooned_pages will only subtract pgno pages, but since
+        * target_unpopulated is incremented with nr_pages at the start we need
+        * to remove the remaining ones also, or accounting will be screwed.
+        */
+       balloon_stats.target_unpopulated -= nr_pages - pgno;
        return ret;
 }
 EXPORT_SYMBOL(alloc_xenballooned_pages);
-- 
2.27.0