Patchwork [2/5] ext4: let ext4 journal deletion of data blocks

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Submitter Yongqiang Yang
Date Nov. 15, 2011, 8:07 a.m.
Message ID <1321344474-14707-2-git-send-email-xiaoqiangnk@gmail.com>
Download mbox | patch
Permalink /patch/125724/
State Rejected
Headers show

Comments

Yongqiang Yang - Nov. 15, 2011, 8:07 a.m.
This patch lets ext4 journal deletion of data blocks. Besides this,
a unnecessary variable is removed.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
---
 fs/ext4/mballoc.c |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)
Theodore Ts'o - Dec. 28, 2011, 5:23 p.m.
On Tue, Nov 15, 2011 at 04:07:51PM +0800, Yongqiang Yang wrote:
> This patch lets ext4 journal deletion of data blocks. Besides this,
> a unnecessary variable is removed.
> 
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>

I don't see the point of this patch; it seems to be a code
simplification, but in fact it introduces a bug which has to get fixed
in patch 3/5 of this series.

The code here is a little arcane, because if bh is non-null, then
count must be 1.  This is expressed in the BUG_ON found in the
function:

>  		BUG_ON(bh && (count > 1));

The reason for this bit of complexity is to avoid needing to call
sb_find_get_block() in those places where we have the buffer_head
already.  This happens in exactly two locations: in an error cleanup
path in fs/ext4/indirect.c, and when releasing an xattr block in
ext4_xattr_release_block().

The better way of dealing with this is to drop the bh argument from
ext4_free_blocks() completely, and explicitly call ext4_forget() on
the bh in those two functions.

This will require changing all of the call sites of
ext4_free_blocks(), but it simplifies the function signature as well
as simplifying the code.

					- Ted

>  fs/ext4/mballoc.c |    7 ++-----
>  1 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index e2d8be8..2529efc 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4562,19 +4562,16 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
>  	trace_ext4_free_blocks(inode, block, count, flags);
>  
>  	if (flags & EXT4_FREE_BLOCKS_FORGET) {
> -		struct buffer_head *tbh = bh;
>  		int i;
>  
>  		BUG_ON(bh && (count > 1));
>  
>  		for (i = 0; i < count; i++) {
>  			if (!bh)
> -				tbh = sb_find_get_block(inode->i_sb,
> +				bh = sb_find_get_block(inode->i_sb,
>  							block + i);
> -			if (unlikely(!tbh))
> -				continue;
>  			ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
> -				    inode, tbh, block + i);
> +				    inode, bh, block + i);
>  		}
>  	}
>  
> -- 
> 1.7.5.1
> 
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Yongqiang Yang - Dec. 30, 2011, 2:59 p.m.
Hi Ted,

The 2nd and 3rd patch aim to let ext4_free_blocks work with journal
mode.  Consider that journal mode of a file is changed from ordered
mode to journal mode and several data blocks are deleted, then bh
passed in is NULL and sb_find_get_block returns NULL, but we need
ext4_forget to handle the data blocks to record them in revoke table.

I am not sure status of ext4 with journal mode, according code here it
seems that ext4 with journal mode does not work.

Yongqiang.

On Thu, Dec 29, 2011 at 1:23 AM, Ted Ts'o <tytso@mit.edu> wrote:
> On Tue, Nov 15, 2011 at 04:07:51PM +0800, Yongqiang Yang wrote:
>> This patch lets ext4 journal deletion of data blocks. Besides this,
>> a unnecessary variable is removed.
>>
>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
>
> I don't see the point of this patch; it seems to be a code
> simplification, but in fact it introduces a bug which has to get fixed
> in patch 3/5 of this series.
>
> The code here is a little arcane, because if bh is non-null, then
> count must be 1.  This is expressed in the BUG_ON found in the
> function:
>
>>               BUG_ON(bh && (count > 1));
>
> The reason for this bit of complexity is to avoid needing to call
> sb_find_get_block() in those places where we have the buffer_head
> already.  This happens in exactly two locations: in an error cleanup
> path in fs/ext4/indirect.c, and when releasing an xattr block in
> ext4_xattr_release_block().
>
> The better way of dealing with this is to drop the bh argument from
> ext4_free_blocks() completely, and explicitly call ext4_forget() on
> the bh in those two functions.
>
> This will require changing all of the call sites of
> ext4_free_blocks(), but it simplifies the function signature as well
> as simplifying the code.
>
>                                        - Ted
>
>>  fs/ext4/mballoc.c |    7 ++-----
>>  1 files changed, 2 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>> index e2d8be8..2529efc 100644
>> --- a/fs/ext4/mballoc.c
>> +++ b/fs/ext4/mballoc.c
>> @@ -4562,19 +4562,16 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
>>       trace_ext4_free_blocks(inode, block, count, flags);
>>
>>       if (flags & EXT4_FREE_BLOCKS_FORGET) {
>> -             struct buffer_head *tbh = bh;
>>               int i;
>>
>>               BUG_ON(bh && (count > 1));
>>
>>               for (i = 0; i < count; i++) {
>>                       if (!bh)
>> -                             tbh = sb_find_get_block(inode->i_sb,
>> +                             bh = sb_find_get_block(inode->i_sb,
>>                                                       block + i);
>> -                     if (unlikely(!tbh))
>> -                             continue;
>>                       ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
>> -                                 inode, tbh, block + i);
>> +                                 inode, bh, block + i);
>>               }
>>       }
>>
>> --
>> 1.7.5.1
>>
Theodore Ts'o - Dec. 30, 2011, 3:05 p.m.
On Fri, Dec 30, 2011 at 10:59:48PM +0800, Yongqiang Yang wrote:
> Hi Ted,
> 
> The 2nd and 3rd patch aim to let ext4_free_blocks work with journal
> mode.  Consider that journal mode of a file is changed from ordered
> mode to journal mode and several data blocks are deleted, then bh
> passed in is NULL and sb_find_get_block returns NULL, but we need
> ext4_forget to handle the data blocks to record them in revoke table.

Ah, I see.  This wasn't obvious from the commit description.  Could
you combine patches #2 and #3, and add the above detail in the commit
description?

Many thanks!!

					- Ted
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Patch

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index e2d8be8..2529efc 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4562,19 +4562,16 @@  void ext4_free_blocks(handle_t *handle, struct inode *inode,
 	trace_ext4_free_blocks(inode, block, count, flags);
 
 	if (flags & EXT4_FREE_BLOCKS_FORGET) {
-		struct buffer_head *tbh = bh;
 		int i;
 
 		BUG_ON(bh && (count > 1));
 
 		for (i = 0; i < count; i++) {
 			if (!bh)
-				tbh = sb_find_get_block(inode->i_sb,
+				bh = sb_find_get_block(inode->i_sb,
 							block + i);
-			if (unlikely(!tbh))
-				continue;
 			ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
-				    inode, tbh, block + i);
+				    inode, bh, block + i);
 		}
 	}