Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1585935 > unrolled thread

[PATCH] mm: do not access page->mapping directly on page_endio

Back to article view | Back to linux.kernel

Contents

  [PATCH] mm: do not access page->mapping directly on page_endio Minchan Kim <minchan@kernel.org> - 2017-02-22 06:40 +0100
    Re: [PATCH] mm: do not access page->mapping directly on page_endio Michal Hocko <mhocko@kernel.org> - 2017-02-22 13:20 +0100
      Re: [PATCH] mm: do not access page->mapping directly on page_endio Minchan Kim <minchan@kernel.org> - 2017-02-22 15:40 +0100
        Re: [PATCH] mm: do not access page->mapping directly on page_endio Michal Hocko <mhocko@kernel.org> - 2017-02-22 16:00 +0100
          Re: [PATCH] mm: do not access page->mapping directly on page_endio Minchan Kim <minchan@kernel.org> - 2017-02-24 00:30 +0100
            Re: [PATCH] mm: do not access page->mapping directly on page_endio Michal Hocko <mhocko@kernel.org> - 2017-02-24 10:20 +0100

#1585935 — [PATCH] 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.

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

[toc] | [next] | [standalone]

#1586114

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

[toc] | [prev] | [next] | [standalone]

#1586214

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.

[toc] | [prev] | [next] | [standalone]

#1586225

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

[toc] | [prev] | [next] | [standalone]

#1587166

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

[toc] | [prev] | [next] | [standalone]

#1587444

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

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web