On Wed, Feb 22, 2017 at 03:53:16PM +0100, Michal Hocko wrote:
> On Wed 22-02-17 23:35:17, Minchan Kim wrote:
> > On Wed, Feb 22, 2017 at 01:11:00PM +0100, Michal Hocko wrote:
> > > 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
> >
> > No. For driver to support rw_page, every swap_writepage calls rw_page.
> >
> > swap_writepage
> > bdev_writepage
> > ops->rw_page
>
> Ohh, you are right, I have missed this option. I was looking at the
> normal swapout path which uses bio.
>
> > > 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?
> >
> > Look at other drivers to support rw_page, not zram, esp, brd.
> > They can be used for swap device and then can hit the case.
> >
> > In fact, I encountered the BUG during zram development(i.e., it doesn't
> > land to upstream) and it was really hard to figure it out because it made
> > random crash, sometime mmap_sem lockdep, sometime other places where
> > places never related to zram/zsmalloc, sometime not reproducible.
> >
> > When I consider how that bug is subtle and people do fast-swap test as brd,
> > it's worth to add stable mark, I think.
>
> Sure, could you add this to the changelog. Along with Fixes tag? I
> suspect it is dd6bd0d9c7db ("swap: use bdev_read_page() /
> bdev_write_page()") which has introduced this but I didn't look too
> close. The patch is trivially correct.
Sure. Thanks for the review.
Andrew, Could you change description with this?
>From 9efb87a873db67a9e6ebf44fdabf7d05fe4b4e21 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@xxxxxxxxxx>
Date: Fri, 4 Nov 2016 09:12:39 +0900
Subject: [PATCH v2] mm: do not access page->mapping directly on page_endio
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.
swap_writepage
bdev_writepage
ops->rw_page
I encountered the BUG during developing new zram feature and
it was really hard to figure it out because it made random
crash, somtime mmap_sem lockdep, sometime other places where
places never related to zram/zsmalloc, and not reproducible
with some configuration.
When I consider how that bug is subtle and people do fast-swap
test with brd, it's worth to add stable mark, I think.
Fixes: dd6bd0d9c7db ("swap: use bdev_read_page() / bdev_write_page()")
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
* from v1
* add more detailed description with Fix tag - Michal
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