Re: [PATCH] mm: do not access page->mapping directly on page_endio
From: Michal Hocko <mhocko@kernel.org>
Date: 2017-02-22 12:11:10
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On Wed 22-02-17 14:39:24, Minchan Kim wrote:
With rw_page, page_endio is used for completing IO on a page and it propagates write error to the address space if the IO fails. The problem is it accesses page->mapping directly which might be okay for file-backed pages but it shouldn't for anonymous page. Otherwise, it can corrupt one of field from anon_vma under us and system goes panic randomly.
I was about to say that anonymous pages shouldn't hit that path because the end_swap_bio_write doesn call page_endio. But then I've noticed that zram does call this function. On a closer look, though, it doesn't seem to call it with err != 0 so it cannot hit this path. So I am wondering whether this actually fixes anything. Why it has been marked for stable?
quoted hunk ↗ jump to hunk
Cc: Matthew Wilcox <willy@infradead.org> Cc: <redacted> Signed-off-by: Minchan Kim <minchan@kernel.org> --- mm/filemap.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)diff --git a/mm/filemap.c b/mm/filemap.c index 2ba46f410c7c..1944c631e3e6 100644 --- a/mm/filemap.c +++ b/mm/filemap.c@@ -1008,9 +1008,12 @@ void page_endio(struct page *page, bool is_write, int err) unlock_page(page); } else { if (err) { + struct address_space *mapping; + SetPageError(page); - if (page->mapping) - mapping_set_error(page->mapping, err); + mapping = page_mapping(page); + if (mapping) + mapping_set_error(mapping, err); } end_page_writeback(page); }-- 2.7.4
-- Michal Hocko SUSE Labs