[PATCH 1/2] ext4: remove a wrong BUG_ON in ext4_ext_convert_to_initialized

[PATCH 1/2] ext4: remove a wrong BUG_ON in ext4_ext_convert_to_initialized

[Yongqiang Yang]

If a file is fallocated on a hole, map->m_lblk + map->m_len may be greater
than ee_block + ee_len.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
---
 fs/ext4/extents.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 6f0300e..29bb629 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2943,7 +2943,6 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
 	/* Pre-conditions */
 	BUG_ON(!ext4_ext_is_uninitialized(ex));
 	BUG_ON(!in_range(map->m_lblk, ee_block, ee_len));
-	BUG_ON(map->m_lblk + map->m_len > ee_block + ee_len);
 
 	/*
 	 * Attempt to transfer newly initialized blocks from the currently
-- 
1.7.5.1

[PATCH 2/2] ext4: let ext4_bio_write_page handle EOF correctly

[Yongqiang Yang]

We need to zero out part of a page which beyond EOF before setting uptodate,
otherwise, mapread or write will see non-zero data beyond EOF.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
---
 fs/ext4/page-io.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 235b79d..9e145b8 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -385,6 +385,18 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
 
 		block_end = block_start + blocksize;
 		if (block_start >= len) {
+			/*
+			 * Comments copied from block_write_full_page_endio:
+			 *
+			 * The page straddles i_size.  It must be zeroed out on
+			 * each and every writepage invocation because it may
+			 * be mmapped.  "A file is mapped in multiples of the
+			 * page size.  For a file that is not a multiple of
+			 * the  page size, the remaining memory is zeroed when
+			 * mapped, and writes to that region are not written
+			 * out to the file."
+			 */
+			zero_user_segment(page, block_start, block_end);
 			clear_buffer_dirty(bh);
 			set_buffer_uptodate(bh);
 			continue;
-- 
1.7.5.1

Re: [PATCH 1/2] ext4: remove a wrong BUG_ON in ext4_ext_convert_to_initialized

[Eric Gouriou]

On Tue, Dec 6, 2011 at 21:21, Yongqiang Yang <xiaoqiangnk@gmail.com> wrote:
> If a file is fallocated on a hole, map->m_lblk + map->m_len may be greater
> than ee_block + ee_len.

Could you please detail a scenario that leads to this check being invalid?
As I'm to blame for the faulty BUG_ON I'd like to use this as an opportunity
to get properly edified.

> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
> ---
>  fs/ext4/extents.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 6f0300e..29bb629 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2943,7 +2943,6 @@ static int ext4_ext_convert_to_initialized(handle_t *handle,
>        /* Pre-conditions */
>        BUG_ON(!ext4_ext_is_uninitialized(ex));
>        BUG_ON(!in_range(map->m_lblk, ee_block, ee_len));
> -       BUG_ON(map->m_lblk + map->m_len > ee_block + ee_len);

For a bit I thought this would break the fast path logic, however it gets
protected by the checks marked /*L1*/ and /*L2*/ since m_lblk == ee_block
(L1) and m_len < ee_len (L2).

 Regards - Eric

>
>        /*
>         * Attempt to transfer newly initialized blocks from the currently
> --
> 1.7.5.1
>
> --
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Re: [PATCH 1/2] ext4: remove a wrong BUG_ON in ext4_ext_convert_to_initialized

[Eric Gouriou]

[Yet another resend, without HTML and _with_ the list CC'ed. Apologies
for the spam]

On Fri, Dec 9, 2011 at 19:36, Yongqiang Yang <xiaoqiangnk@gmail.com> wrote:
>
>
> On Saturday, December 10, 2011, Eric Gouriou <egouriou@google.com> wrote:
>> On Tue, Dec 6, 2011 at 21:21, Yongqiang Yang <xiaoqiangnk@gmail.com>
>> wrote:
>>> If a file is fallocated on a hole, map->m_lblk + map->m_len may be
>>> greater
>>> than ee_block + ee_len.
>>
>> Could you please detail a scenario that leads to this check being invalid?
>> As I'm to blame for the faulty BUG_ON I'd like to use this as an
>> opportunity
>> to get properly edified.
> It's easy to reproduce, I think.   Just need to write beyond fallocated
> blocks, write back would submit a request to ext4_map_blocks with blocks
> part of which are fallocated while other part of which are not, then the
> bug-on would happen.

Thanks, this makes sense.

>
> I met the bug_on during fsx and after the patch applied it works normal.
>
> I think Allison also tested with this patch.
>
> Yongqiang..
>
>>
>>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>

Reviewed-by: Eric Gouriou <egouriou@google.com>

 Thanks - Eric

>>> ---
>>>  fs/ext4/extents.c |    1 -
>>>  1 files changed, 0 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>>> index 6f0300e..29bb629 100644
>>> --- a/fs/ext4/extents.c
>>> +++ b/fs/ext4/extents.c
>>> @@ -2943,7 +2943,6 @@ static int ext4_ext_convert_to_initialized(handle_t
>>> *handle,
>>>        /* Pre-conditions */
>>>        BUG_ON(!ext4_ext_is_uninitialized(ex));
>>>        BUG_ON(!in_range(map->m_lblk, ee_block, ee_len));
>>> -       BUG_ON(map->m_lblk + map->m_len > ee_block + ee_len);
>>
>> For a bit I thought this would break the fast path logic, however it gets
>> protected by the checks marked /*L1*/ and /*L2*/ since m_lblk == ee_block
>> (L1) and m_len < ee_len (L2).
>>
>>  Regards - Eric
>>
>>>
>>>        /*
>>>         * Attempt to transfer newly initialized blocks from the currently
>>> --
>>> 1.7.5.1
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
> --
> Best Wishes
> Yongqiang Yang
>
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Re: [PATCH 1/2] ext4: remove a wrong BUG_ON in ext4_ext_convert_to_initialized

[Ted Ts'o]

On Wed, Dec 07, 2011 at 01:21:26PM +0800, Yongqiang Yang wrote:
> If a file is fallocated on a hole, map->m_lblk + map->m_len may be greater
> than ee_block + ee_len.
> 
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>

Thanks, applied.

					- Ted

Re: [PATCH 2/2] ext4: let ext4_bio_write_page handle EOF correctly

[Ted Ts'o]

On Wed, Dec 07, 2011 at 01:21:27PM +0800, Yongqiang Yang wrote:
> We need to zero out part of a page which beyond EOF before setting uptodate,
> otherwise, mapread or write will see non-zero data beyond EOF.
> 
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>

Thanks, applied.

						- Ted