2020-07-24 12:44:41

by Roger Pau Monne

Subject: [PATCH v2 1/4] 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 <[email protected]>
Cc: [email protected]
---
Cc: Boris Ostrovsky <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: [email protected]
---
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

2020-07-24 13:14:41

by Jürgen Groß

Subject: Re: [PATCH v2 1/4] xen/balloon: fix accounting in alloc_xenballooned_pages error path

On 24.07.20 14:42, Roger Pau Monne wrote:
> 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 <[email protected]>

Reviewed-by: Juergen Gross <[email protected]>


Juergen