Btrfs devel - Nov 2009 - [patch] avoid null deref in unpin_extent_cache()

I re-orderred the checks to avoid dereferencing "em" if it was null.

Found by smatch static checker.

regards,
dan carpenter

Signed-off-by: Dan Carpenter <error27@gmail.com>

--- orig/fs/btrfs/extent_map.c	2009-11-08 14:01:09.000000000 +0200
+++ devel/fs/btrfs/extent_map.c	2009-11-08 14:01:44.000000000 +0200
@@ -208,7 +208,7 @@
 	write_lock(&tree->lock);
 	em = lookup_extent_mapping(tree, start, len);
 
-	WARN_ON(em->start != start || !em);
+	WARN_ON(!em || em->start != start);
 
 	if (!em)
 		goto out;
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On Tue, Nov 10, 2009 at 11:01:43AM +0200, Dan Carpenter
wrote:
> I re-orderred the checks to avoid dereferencing "em" if it was
null.
Thanks, I''ve put this into the master branch of the btrfs unstable
tree.

-chris
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