xen/balloon: fix accounting in alloc_xenballooned_pages error path

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@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200727091342.52325-2-roger.pau@citrix.com
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 77c5756..3cb10ed 100644 (file)
--- 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);