[PATCH] ext4: Fix the loop condition in ext4_mb_free_committed_blocks

[PATCH] ext4: Fix the loop condition in ext4_mb_free_committed_blocks

[Shen Feng]

Since md is freed before the do-while checks it,
it's better to change it to while(1).

Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
---
 fs/ext4/mballoc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 42553f6..063f820 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2572,7 +2572,7 @@ ext4_mb_free_committed_blocks(struct super_block *sb)
 		kfree(md);
 		ext4_mb_release_desc(&e4b);
 
-	} while (md);
+	} while (1);
 
 	mb_debug("freed %u blocks in %u structures\n", count, count2);
 }
-- 
1.5.4.5

Re: [PATCH] ext4: Fix the loop condition in ext4_mb_free_committed_blocks

[Aneesh Kumar K.V]

On Wed, Jun 11, 2008 at 11:55:45AM +0800, Shen Feng wrote:
> 
> Since md is freed before the do-while checks it,
> it's better to change it to while(1).
> 
> Signed-off-by: Shen Feng <shen@cn.fujitsu.com>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> ---
>  fs/ext4/mballoc.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 42553f6..063f820 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2572,7 +2572,7 @@ ext4_mb_free_committed_blocks(struct super_block *sb)
>  		kfree(md);
>  		ext4_mb_release_desc(&e4b);
> 
> -	} while (md);
> +	} while (1);
> 
>  	mb_debug("freed %u blocks in %u structures\n", count, count2);
>  }
> -- 
> 1.5.4.5
> --
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Re: [PATCH] ext4: Fix the loop condition in ext4_mb_free_committed_blocks

[Theodore Tso]

On Wed, Jun 11, 2008 at 11:55:45AM +0800, Shen Feng wrote:
> 
> Since md is freed before the do-while checks it,
> it's better to change it to while(1).

This actually isn't a bug, since there is no problem checking a
pointer that has been freed; its only *dereferencing* a pointer which
is bad.  That being said, md is never NULL at the end of the loop,
since in the middle of the loop is the only break condition:

	if (md == NULL)
		break;

So the patch saves a tiny amount of compiled code, but it isn't really
a fix in any way.

That being said, if we're going to make this sort of change, my
preference would be to use the more common C idiom:

	while (1) {
	      ...
	}

as opposed to

	do {
	      ...
	} while (1);

The former makes it quite clear that any exit from the loop is not
going to be coming from loop construct itself, but from any embedded
break statements inside the loop construct

Regards,

						- Ted

[PATCH V2] ext4: Fix the loop condition in ext4_mb_free_committed_blocks

[Shen Feng]

>> Since md is freed before the do-while checks it,
>> it's better to change it to while(1).
> 
> This actually isn't a bug, since there is no problem checking a
> pointer that has been freed; its only *dereferencing* a pointer which
> is bad.  That being said, md is never NULL at the end of the loop,
> since in the middle of the loop is the only break condition:
> 
> 	if (md == NULL)
> 		break;
> 
> So the patch saves a tiny amount of compiled code, but it isn't really
> a fix in any way.
> 
> That being said, if we're going to make this sort of change, my
> preference would be to use the more common C idiom:
> 
> 	while (1) {
> 	      ...
> 	}
> 
> as opposed to
> 
> 	do {
> 	      ...
> 	} while (1);
> 
> The former makes it quite clear that any exit from the loop is not
> going to be coming from loop construct itself, but from any embedded
> break statements inside the loop construct
> 

Yes. You are right. Revise the patch as you suggested.

Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
---
 fs/ext4/mballoc.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index c9900aa..bd6cf22 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2521,7 +2521,7 @@ ext4_mb_free_committed_blocks(struct super_block *sb)
 		return;
 
 	/* there is committed blocks to be freed yet */
-	do {
+	while (1) {
 		/* get next array of blocks */
 		md = NULL;
 		spin_lock(&sbi->s_md_lock);
@@ -2561,7 +2561,7 @@ ext4_mb_free_committed_blocks(struct super_block *sb)
 		kfree(md);
 		ext4_mb_release_desc(&e4b);
 
-	} while (md);
+	}
 
 	mb_debug("freed %u blocks in %u structures\n", count, count2);
 }
-- 1.5.4.5