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    Subject[PATCH 4.19 166/168] xen/balloon: fix accounting in alloc_xenballooned_pages error path
    Date
    From: Roger Pau Monne <roger.pau@citrix.com>

    commit 1951fa33ec259abdf3497bfee7b63e7ddbb1a394 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/xen/balloon.c | 6 ++++++
    1 file changed, 6 insertions(+)

    --- a/drivers/xen/balloon.c
    +++ b/drivers/xen/balloon.c
    @@ -632,6 +632,12 @@ int alloc_xenballooned_pages(int nr_page
    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);

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