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From:   Roger Pau Monne <roger.pau@citrix.com>
To:     <linux-kernel@vger.kernel.org>
CC:     Roger Pau Monne <roger.pau@citrix.com>,
        Juergen Gross <jgross@suse.com>, <stable@vger.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        <xen-devel@lists.xenproject.org>
Subject: [PATCH v3 1/4] xen/balloon: fix accounting in alloc_xenballooned_pages error path
Date:   Mon, 27 Jul 2020 11:13:39 +0200
Message-ID: <20200727091342.52325-2-roger.pau@citrix.com>
In-Reply-To: <20200727091342.52325-1-roger.pau@citrix.com>
References: <20200727091342.52325-1-roger.pau@citrix.com>
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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
---
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org
---
 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