Patchwork ext4: signedness bug breaks ext4_inode_touch_time_cmp()

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Submitter Theodore Ts'o
Date June 20, 2013, 2:13 p.m.
Message ID <20130620141310.GB28309@thunk.org>
Download mbox | patch
Permalink /patch/252942/
State Accepted
Headers show

Comments

Theodore Ts'o - June 20, 2013, 2:13 p.m.
On Thu, Jun 20, 2013 at 11:08:58AM +0300, Dan Carpenter wrote:
> "diff" is unsigned so this doesn't sort the LRU list correctly.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This was introduced in 6480bad916be "ext4: improve extent cache shrink
> mechanism to avoid to burn CPU time"

Thanks for pointing this out!  The following patch is better I think
because it uses the time_after() abstraction.  I will be folding the
following into Zheng's "ext4: improve extent cache shrink > mechanism
to avoid to burn CPU time".

I've desk checked this but we may want to do some explicit testing to
make sure we are in fact ejecting the appropriate inode from the list.

     	     	    	 	      - Ted

 fs/ext4/extents_status.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

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Zheng Liu - June 20, 2013, 3:24 p.m.
On Thu, Jun 20, 2013 at 10:13:10AM -0400, Theodore Ts'o wrote:
> On Thu, Jun 20, 2013 at 11:08:58AM +0300, Dan Carpenter wrote:
> > "diff" is unsigned so this doesn't sort the LRU list correctly.
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > This was introduced in 6480bad916be "ext4: improve extent cache shrink
> > mechanism to avoid to burn CPU time"
> 
> Thanks for pointing this out!  The following patch is better I think
> because it uses the time_after() abstraction.  I will be folding the
> following into Zheng's "ext4: improve extent cache shrink > mechanism
> to avoid to burn CPU time".

Thanks for fixing it.  The patch looks good to me.
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>

> 
> I've desk checked this but we may want to do some explicit testing to
> make sure we are in fact ejecting the appropriate inode from the list.

I will check it tomorrow.  If there still has a problem, I will try to
fix it.

                                                - Zheng

> 
>      	     	    	 	      - Ted
> 
>  fs/ext4/extents_status.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
> index 80dcc59..ee018d5 100644
> --- a/fs/ext4/extents_status.c
> +++ b/fs/ext4/extents_status.c
> @@ -880,17 +880,15 @@ static int ext4_inode_touch_time_cmp(void *priv, struct list_head *a,
>  				     struct list_head *b)
>  {
>  	struct ext4_inode_info *eia, *eib;
> -	unsigned long diff;
> -
>  	eia = list_entry(a, struct ext4_inode_info, i_es_lru);
>  	eib = list_entry(b, struct ext4_inode_info, i_es_lru);
>  
> -	diff = eia->i_touch_when - eib->i_touch_when;
> -	if (diff < 0)
> -		return -1;
> -	if (diff > 0)
> +	if (eia->i_touch_when == eib->i_touch_when)
> +		return 0;
> +	if (time_after(eia->i_touch_when, eib->i_touch_when))
>  		return 1;
> -	return 0;
> +	else
> +		return -1;
>  }
>  
>  static int ext4_es_shrink(struct shrinker *shrink, struct shrink_control *sc)
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Patch

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 80dcc59..ee018d5 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -880,17 +880,15 @@  static int ext4_inode_touch_time_cmp(void *priv, struct list_head *a,
 				     struct list_head *b)
 {
 	struct ext4_inode_info *eia, *eib;
-	unsigned long diff;
-
 	eia = list_entry(a, struct ext4_inode_info, i_es_lru);
 	eib = list_entry(b, struct ext4_inode_info, i_es_lru);
 
-	diff = eia->i_touch_when - eib->i_touch_when;
-	if (diff < 0)
-		return -1;
-	if (diff > 0)
+	if (eia->i_touch_when == eib->i_touch_when)
+		return 0;
+	if (time_after(eia->i_touch_when, eib->i_touch_when))
 		return 1;
-	return 0;
+	else
+		return -1;
 }
 
 static int ext4_es_shrink(struct shrinker *shrink, struct shrink_control *sc)