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SubjectRe: [PATCH 2/2] perf/x86/intel/bts: Fix the use of page_private()
On Thu, Dec 05, 2019 at 05:28:53PM +0300, Alexander Shishkin wrote:
> Commit
>
> 8062382c8dbe2 ("perf/x86/intel/bts: Add BTS PMU driver")
>
> uses page_private(page) without checking the PagePrivate(page) first,
> which seems like a potential bug, considering that page->private aliases
> with other stuff in struct page.
>
> Fix this by checking PagePrivate() first.
>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Fixes: 8062382c8dbe2 ("perf/x86/intel/bts: Add BTS PMU driver")
> ---
> arch/x86/events/intel/bts.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
> index d53b4fb86d87..9e4da1c5a129 100644
> --- a/arch/x86/events/intel/bts.c
> +++ b/arch/x86/events/intel/bts.c
> @@ -63,9 +63,17 @@ struct bts_buffer {
>
> static struct pmu bts_pmu;
>
> +static int buf_nr_pages(struct page *page)
> +{
> + if (!PagePrivate(page))
> + return 1;
> +
> + return 1 << page_private(page);
> +}
> +
> static size_t buf_size(struct page *page)
> {
> - return 1 << (PAGE_SHIFT + page_private(page));
> + return 1 << (PAGE_SHIFT + buf_nr_pages(page));

Hurmph, shouldn't that be:

return buf_nr_pages(page) * PAGE_SIZE;

?

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