Re: [PATCH] mm/debug: PageAnon() is true for PageKsm() pages

Michal Hocko
2019-11-14T13:59:51Z

On Tue 12-11-19 16:06:51, Ralph Campbell wrote:
> PageAnon() and PageKsm() use the low two bits of the page->mapping pointer
> to indicate the page type. PageAnon() only checks the LSB while PageKsm()
> checks the least significant 2 bits are equal to 3. Therefore, PageAnon()
> is true for KSM pages.
> __dump_page() incorrectly will never print "ksm" because it checks
> PageAnon() first. Fix this by checking PageKsm() first.

Thanks for spotting this

Fixes: 1c6fb1d89e73 ("mm: print more information about mapping in __dump_page")

> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> mm/debug.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/debug.c b/mm/debug.c
> index 772d4cf0691f..0461df1207cb 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -77,10 +77,10 @@ void __dump_page(struct page *page, const char *reason)
> pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n",
> page, page_ref_count(page), mapcount,
> page->mapping, page_to_pgoff(page));
> - if (PageAnon(page))
> - pr_warn("anon flags: %#lx(%pGp)\n", page->flags, &page->flags);
> - else if (PageKsm(page))
> + if (PageKsm(page))
> pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags);
> + else if (PageAnon(page))
> + pr_warn("anon flags: %#lx(%pGp)\n", page->flags, &page->flags);
> else if (mapping) {
> if (mapping->host && mapping->host->i_dentry.first) {
> struct dentry *dentry;
> --
> 2.20.1

--
Michal Hocko
SUSE Labs