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

Commit Message

Roger Pau Monné July 27, 2020, 9:13 a.m. UTC

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 <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Cc: [e-mail]
---
Cc: Boris Ostrovsky <[e-mail]>
Cc: Juergen Gross <[e-mail]>
Cc: Stefano Stabellini <[e-mail]>
Cc: [e-mail]
---
 drivers/xen/balloon.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Jürgen Groß Aug. 3, 2020, 6:18 a.m. UTC | #1

On 27.07.20 11:13, 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 <[e-mail]>
> Reviewed-by: Juergen Gross <[e-mail]>
> Cc: [e-mail]

Pushed to xen/tip.git for-linus-5.9


Juergen

Patch

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);