Re: Bad use of highmem with buffer_migrate_page?

Re: Bad use of highmem with buffer_migrate_page?

[Rabin Vincent]

On Sat, May 12, 2012 at 3:21 AM, Laura Abbott <lauraa@codeaurora.org> wrote:
> On 5/11/2012 1:30 AM, Marek Szyprowski wrote:
>> On Thursday, May 10, 2012 10:08 PM Laura Abbott wrote:
>>> I did a backport of the Contiguous Memory Allocator to a 3.0.8 tree. I
>>> wrote fairly simple test case that, in 1MB chunks, allocs up to 40MB
>>> from a reserved area, maps, writes, unmaps and then frees in an infinite
>>> loop. When running this with another program in parallel to put some
>>> stress on the filesystem, I hit data aborts in the filesystem/journal
>>> layer, although not always the same backtrace. As an example:
>>>
>>> [<c02907a4>] (__ext4_check_dir_entry+0x20/0x184) from [<c029e1a8>]
>>> (add_dirent_to_buf+0x70/0x2ac)
>>> [<c029e1a8>] (add_dirent_to_buf+0x70/0x2ac) from [<c029f3f0>]
>>> (ext4_add_entry+0xd8/0x4bc)
>>> [<c029f3f0>] (ext4_add_entry+0xd8/0x4bc) from [<c029fe90>]
>>> (ext4_add_nondir+0x14/0x64)
>>> [<c029fe90>] (ext4_add_nondir+0x14/0x64) from [<c02a04c4>]
>>> (ext4_create+0xd8/0x120)
>>> [<c02a04c4>] (ext4_create+0xd8/0x120) from [<c022e134>]
>>> (vfs_create+0x74/0xa4)
>>> [<c022e134>] (vfs_create+0x74/0xa4) from [<c022ed3c>]
>>> (do_last+0x588/0x8d4)
>>> [<c022ed3c>] (do_last+0x588/0x8d4) from [<c022fe64>]
>>> (path_openat+0xc4/0x394)
>>> [<c022fe64>] (path_openat+0xc4/0x394) from [<c0230214>]
>>> (do_filp_open+0x30/0x7c)
>>> [<c0230214>] (do_filp_open+0x30/0x7c) from [<c0220cb4>]
>>> (do_sys_open+0xd8/0x174)
>>> [<c0220cb4>] (do_sys_open+0xd8/0x174) from [<c0105ea0>]
>>> (ret_fast_syscall+0x0/0x30)
>>>
>>> Every panic had the same issue where a struct buffer_head [1] had a
>>> b_data that was unexpectedly NULL.
>>>
>>> During the course of CMA, buffer_migrate_page could be called to migrate
>>> from a CMA page to a new page. buffer_migrate_page calls set_bh_page[2]
>>> to set the new page for the buffer_head. If the new page is a highmem
>>> page though, the bh->b_data ends up as NULL, which could produce the
>>> panics seen above.
>>>
>>> This seems to indicate that highmem pages are not not appropriate for
>>> use as pages to migrate to. The following made the problem go away for
>>> me:
>>>
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -5753,7 +5753,7 @@ static struct page *
>>>    __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
>>>                                int **resultp)
>>>    {
>>> -       return alloc_page(GFP_HIGHUSER_MOVABLE);
>>> +       return alloc_page(GFP_USER | __GFP_MOVABLE);
>>>    }
>>>
>>>
>>> Does this seem like an actual issue or is this an artifact of my
>>> backport to 3.0? I'm not familiar enough with the filesystem layer to be
>>> able to tell where highmem can actually be used.
>>
>>
>> I will need to investigate this further as this issue doesn't appear on
>> v3.3+ kernels, but I remember I saw something similar when I tried CMA
>> backported to v3.0.

The problem is still present on latest mainline.  The filesystem layer
expects that the pages in the block device's mapping are not in highmem
(the mapping's gfp mask is set in bdget()), but CMA replaces lowmem
pages with highmem pages leading to the crashes.

The above fix should work, but perhaps the following is preferable since
it should allow moving highmem pages to other highmem pages?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4403009..4a4f921 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5635,7 +5635,12 @@ static struct page *
 __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
 			     int **resultp)
 {
-	return alloc_page(GFP_HIGHUSER_MOVABLE);
+	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
+
+	if (PageHighMem(page))
+		gfp_mask |= __GFP_HIGHMEM;
+
+	return alloc_page(gfp_mask);
 }

 /* [start, end) must belong to a single zone. */

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RE: Bad use of highmem with buffer_migrate_page?

[Marek Szyprowski]

Hello,

On Thursday, July 05, 2012 11:28 AM Rabin Vincent wrote:

> On Sat, May 12, 2012 at 3:21 AM, Laura Abbott <lauraa@codeaurora.org> wrote:
> > On 5/11/2012 1:30 AM, Marek Szyprowski wrote:
> >> On Thursday, May 10, 2012 10:08 PM Laura Abbott wrote:
> >>> I did a backport of the Contiguous Memory Allocator to a 3.0.8 tree. I
> >>> wrote fairly simple test case that, in 1MB chunks, allocs up to 40MB
> >>> from a reserved area, maps, writes, unmaps and then frees in an infinite
> >>> loop. When running this with another program in parallel to put some
> >>> stress on the filesystem, I hit data aborts in the filesystem/journal
> >>> layer, although not always the same backtrace. As an example:
> >>>
> >>> [<c02907a4>] (__ext4_check_dir_entry+0x20/0x184) from [<c029e1a8>]
> >>> (add_dirent_to_buf+0x70/0x2ac)
> >>> [<c029e1a8>] (add_dirent_to_buf+0x70/0x2ac) from [<c029f3f0>]
> >>> (ext4_add_entry+0xd8/0x4bc)
> >>> [<c029f3f0>] (ext4_add_entry+0xd8/0x4bc) from [<c029fe90>]
> >>> (ext4_add_nondir+0x14/0x64)
> >>> [<c029fe90>] (ext4_add_nondir+0x14/0x64) from [<c02a04c4>]
> >>> (ext4_create+0xd8/0x120)
> >>> [<c02a04c4>] (ext4_create+0xd8/0x120) from [<c022e134>]
> >>> (vfs_create+0x74/0xa4)
> >>> [<c022e134>] (vfs_create+0x74/0xa4) from [<c022ed3c>]
> >>> (do_last+0x588/0x8d4)
> >>> [<c022ed3c>] (do_last+0x588/0x8d4) from [<c022fe64>]
> >>> (path_openat+0xc4/0x394)
> >>> [<c022fe64>] (path_openat+0xc4/0x394) from [<c0230214>]
> >>> (do_filp_open+0x30/0x7c)
> >>> [<c0230214>] (do_filp_open+0x30/0x7c) from [<c0220cb4>]
> >>> (do_sys_open+0xd8/0x174)
> >>> [<c0220cb4>] (do_sys_open+0xd8/0x174) from [<c0105ea0>]
> >>> (ret_fast_syscall+0x0/0x30)
> >>>
> >>> Every panic had the same issue where a struct buffer_head [1] had a
> >>> b_data that was unexpectedly NULL.
> >>>
> >>> During the course of CMA, buffer_migrate_page could be called to migrate
> >>> from a CMA page to a new page. buffer_migrate_page calls set_bh_page[2]
> >>> to set the new page for the buffer_head. If the new page is a highmem
> >>> page though, the bh->b_data ends up as NULL, which could produce the
> >>> panics seen above.
> >>>
> >>> This seems to indicate that highmem pages are not not appropriate for
> >>> use as pages to migrate to. The following made the problem go away for
> >>> me:
> >>>
> >>> --- a/mm/page_alloc.c
> >>> +++ b/mm/page_alloc.c
> >>> @@ -5753,7 +5753,7 @@ static struct page *
> >>>    __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
> >>>                                int **resultp)
> >>>    {
> >>> -       return alloc_page(GFP_HIGHUSER_MOVABLE);
> >>> +       return alloc_page(GFP_USER | __GFP_MOVABLE);
> >>>    }
> >>>
> >>>
> >>> Does this seem like an actual issue or is this an artifact of my
> >>> backport to 3.0? I'm not familiar enough with the filesystem layer to be
> >>> able to tell where highmem can actually be used.
> >>
> >>
> >> I will need to investigate this further as this issue doesn't appear on
> >> v3.3+ kernels, but I remember I saw something similar when I tried CMA
> >> backported to v3.0.
> 
> The problem is still present on latest mainline.  The filesystem layer
> expects that the pages in the block device's mapping are not in highmem
> (the mapping's gfp mask is set in bdget()), but CMA replaces lowmem
> pages with highmem pages leading to the crashes.
> 
> The above fix should work, but perhaps the following is preferable since
> it should allow moving highmem pages to other highmem pages?

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4403009..4a4f921 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5635,7 +5635,12 @@ static struct page *
>  __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
>  			     int **resultp)
>  {
> -	return alloc_page(GFP_HIGHUSER_MOVABLE);
> +	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
> +
> +	if (PageHighMem(page))
> +		gfp_mask |= __GFP_HIGHMEM;
> +
> +	return alloc_page(gfp_mask);
>  }
> 
>  /* [start, end) must belong to a single zone. */


The patch looks fine and does it job well. Could you resend it as a complete 
patch with commit message and signed-off-by/reported-by lines? I will handle
merging it to mainline then.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center



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Re: Bad use of highmem with buffer_migrate_page?

[Rabin Vincent]

On Thu, Jul 05, 2012 at 12:05:45PM +0200, Marek Szyprowski wrote:
> On Thursday, July 05, 2012 11:28 AM Rabin Vincent wrote:
> > The problem is still present on latest mainline.  The filesystem layer
> > expects that the pages in the block device's mapping are not in highmem
> > (the mapping's gfp mask is set in bdget()), but CMA replaces lowmem
> > pages with highmem pages leading to the crashes.
> > 
> > The above fix should work, but perhaps the following is preferable since
> > it should allow moving highmem pages to other highmem pages?
> 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 4403009..4a4f921 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5635,7 +5635,12 @@ static struct page *
> >  __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
> >  			     int **resultp)
> >  {
> > -	return alloc_page(GFP_HIGHUSER_MOVABLE);
> > +	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
> > +
> > +	if (PageHighMem(page))
> > +		gfp_mask |= __GFP_HIGHMEM;
> > +
> > +	return alloc_page(gfp_mask);
> >  }
> > 
> >  /* [start, end) must belong to a single zone. */
> 
> 
> The patch looks fine and does it job well. Could you resend it as a complete 
> patch with commit message and signed-off-by/reported-by lines? I will handle
> merging it to mainline then.

Thanks, here it is:

8<----

Re: Bad use of highmem with buffer_migrate_page?

[Cong Wang]

On Thu, 05 Jul 2012 at 10:45 GMT, Rabin Vincent <rabin@rab.in> wrote:
> 8<----
> From 8a94126eb3aa2824866405fb78bb0b8316f8fd00 Mon Sep 17 00:00:00 2001
> From: Rabin Vincent <rabin@rab.in>
> Date: Thu, 5 Jul 2012 15:52:23 +0530
> Subject: [PATCH] mm: cma: don't replace lowmem pages with highmem
>
> The filesystem layer expects pages in the block device's mapping to not
> be in highmem (the mapping's gfp mask is set in bdget()), but CMA can
> currently replace lowmem pages with highmem pages, leading to crashes in
> filesystem code such as the one below:
>
...
> Fix this by replacing only highmem pages with highmem.
>

Looks good to me too,

    Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>

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Re: Bad use of highmem with buffer_migrate_page?

[Michał Nazarewicz]

2012/7/5 Rabin Vincent <rabin@rab.in>:
> From 8a94126eb3aa2824866405fb78bb0b8316f8fd00 Mon Sep 17 00:00:00 2001
> From: Rabin Vincent <rabin@rab.in>
> Date: Thu, 5 Jul 2012 15:52:23 +0530
> Subject: [PATCH] mm: cma: don't replace lowmem pages with highmem
>
> The filesystem layer expects pages in the block device's mapping to not
> be in highmem (the mapping's gfp mask is set in bdget()), but CMA can
> currently replace lowmem pages with highmem pages, leading to crashes in
> filesystem code such as the one below:
>
>   Unable to handle kernel NULL pointer dereference at virtual address 00000400
>   pgd = c0c98000
>   [00000400] *pgd=00c91831, *pte=00000000, *ppte=00000000
>   Internal error: Oops: 817 [#1] PREEMPT SMP ARM
>   CPU: 0    Not tainted  (3.5.0-rc5+ #80)
>   PC is at __memzero+0x24/0x80
>   ...
>   Process fsstress (pid: 323, stack limit = 0xc0cbc2f0)
>   Backtrace:
>   [<c010e3f0>] (ext4_getblk+0x0/0x180) from [<c010e58c>] (ext4_bread+0x1c/0x98)
>   [<c010e570>] (ext4_bread+0x0/0x98) from [<c0117944>] (ext4_mkdir+0x160/0x3bc)
>    r4:c15337f0
>   [<c01177e4>] (ext4_mkdir+0x0/0x3bc) from [<c00c29e0>] (vfs_mkdir+0x8c/0x98)
>   [<c00c2954>] (vfs_mkdir+0x0/0x98) from [<c00c2a60>] (sys_mkdirat+0x74/0xac)
>    r6:00000000 r5:c152eb40 r4:000001ff r3:c14b43f0
>   [<c00c29ec>] (sys_mkdirat+0x0/0xac) from [<c00c2ab8>] (sys_mkdir+0x20/0x24)
>    r6:beccdcf0 r5:00074000 r4:beccdbbc
>   [<c00c2a98>] (sys_mkdir+0x0/0x24) from [<c000e3c0>] (ret_fast_syscall+0x0/0x30)
>
> Fix this by replacing only highmem pages with highmem.
>
> Reported-by: Laura Abbott <lauraa@codeaurora.org>
> Signed-off-by: Rabin Vincent <rabin@rab.in>

Acked-by: Michal Nazarewicz <mina86@mina86.com>

> ---
>  mm/page_alloc.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4403009..4a4f921 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5635,7 +5635,12 @@ static struct page *
>  __alloc_contig_migrate_alloc(struct page *page, unsigned long private,
>                              int **resultp)
>  {
> -       return alloc_page(GFP_HIGHUSER_MOVABLE);
> +       gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
> +
> +       if (PageHighMem(page))
> +               gfp_mask |= __GFP_HIGHMEM;
> +
> +       return alloc_page(gfp_mask);
>  }
>
>  /* [start, end) must belong to a single zone. */

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