* [PATCH] mm: do not access page->mapping directly on page_endio
@ 2017-02-22 5:39 Minchan Kim
2017-02-22 12:11 ` Michal Hocko
0 siblings, 1 reply; 6+ messages in thread
From: Minchan Kim @ 2017-02-22 5:39 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-kernel, kernel-team, Minchan Kim, Matthew Wilcox, stable
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.
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>
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
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: do not access page->mapping directly on page_endio
2017-02-22 5:39 [PATCH] mm: do not access page->mapping directly on page_endio Minchan Kim
@ 2017-02-22 12:11 ` Michal Hocko
2017-02-22 14:35 ` Minchan Kim
0 siblings, 1 reply; 6+ messages in thread
From: Michal Hocko @ 2017-02-22 12:11 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, linux-kernel, kernel-team, Matthew Wilcox, stable
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?
>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: <stable@vger.kernel.org>
> 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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: do not access page->mapping directly on page_endio
2017-02-22 12:11 ` Michal Hocko
@ 2017-02-22 14:35 ` Minchan Kim
2017-02-22 14:53 ` Michal Hocko
0 siblings, 1 reply; 6+ messages in thread
From: Minchan Kim @ 2017-02-22 14:35 UTC (permalink / raw)
To: Michal Hocko
Cc: Andrew Morton, linux-kernel, kernel-team, Matthew Wilcox, stable
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
> 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.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: do not access page->mapping directly on page_endio
2017-02-22 14:35 ` Minchan Kim
@ 2017-02-22 14:53 ` Michal Hocko
2017-02-23 23:26 ` Minchan Kim
0 siblings, 1 reply; 6+ messages in thread
From: Michal Hocko @ 2017-02-22 14:53 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, linux-kernel, kernel-team, Matthew Wilcox, stable
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.
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: do not access page->mapping directly on page_endio
2017-02-22 14:53 ` Michal Hocko
@ 2017-02-23 23:26 ` Minchan Kim
2017-02-24 9:13 ` Michal Hocko
0 siblings, 1 reply; 6+ messages in thread
From: Minchan Kim @ 2017-02-23 23:26 UTC (permalink / raw)
To: Michal Hocko
Cc: Andrew Morton, linux-kernel, kernel-team, Matthew Wilcox, stable
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@kernel.org>
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@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
* 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
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] mm: do not access page->mapping directly on page_endio
2017-02-23 23:26 ` Minchan Kim
@ 2017-02-24 9:13 ` Michal Hocko
0 siblings, 0 replies; 6+ messages in thread
From: Michal Hocko @ 2017-02-24 9:13 UTC (permalink / raw)
To: Minchan Kim
Cc: Andrew Morton, linux-kernel, kernel-team, Matthew Wilcox, stable
On Fri 24-02-17 08:26:09, Minchan Kim wrote:
[...]
> >From 9efb87a873db67a9e6ebf44fdabf7d05fe4b4e21 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> 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@kernel.org>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks for the chagelog update
> ---
> * 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
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 6+ messages in thread
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2017-02-22 5:39 [PATCH] mm: do not access page->mapping directly on page_endio Minchan Kim
2017-02-22 12:11 ` Michal Hocko
2017-02-22 14:35 ` Minchan Kim
2017-02-22 14:53 ` Michal Hocko
2017-02-23 23:26 ` Minchan Kim
2017-02-24 9:13 ` Michal Hocko
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