linux-ext4 - Re: [patch] ext4: signedness bug breaks ext4_inode_touch_time

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Date:	Thu, 20 Jun 2013 10:13:10 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Zheng Liu <wenqing.lz@...bao.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] ext4: signedness bug breaks ext4_inode_touch_time_cmp()

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@...cle.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(-)

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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