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Date: Mon, 22 Apr 2013 16:04:09 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Chen Gang <gang.chen@asianux.com>
Cc: Eric Paris <eparis@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] kernel/audit_tree.c: tree will memory leak when failure
 occurs for audit_trim_trees()
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On Fri, 19 Apr 2013 17:39:06 +0800 Chen Gang <gang.chen@asianux.com> wrote:

> 
> in audit_trim_trees(), has called get_tree() before failure occurs,
> so need also call put_tree after go to skip_it:
> 
> ...
>
> --- a/kernel/audit_tree.c
> +++ b/kernel/audit_tree.c
> @@ -617,10 +617,10 @@ void audit_trim_trees(void)
>  		}
>  		spin_unlock(&hash_lock);
>  		trim_marked(tree);
> -		put_tree(tree);
>  		drop_collected_mounts(root_mnt);
>  skip_it:
>  		mutex_lock(&audit_filter_mutex);
> +		put_tree(tree);
>  	}
>  	list_del(&cursor);
>  	mutex_unlock(&audit_filter_mutex);

That looks right to me.

I think we can micro-optimise the code by performing the put_tree()
before taking the mutex, to slightly reduce mutex hold times?

--- a/kernel/audit_tree.c~kernel-audit_treec-tree-will-leak-memory-when-failure-occurs-in-audit_trim_trees-fix
+++ a/kernel/audit_tree.c
@@ -619,8 +619,8 @@ void audit_trim_trees(void)
 		trim_marked(tree);
 		drop_collected_mounts(root_mnt);
 skip_it:
-		mutex_lock(&audit_filter_mutex);
 		put_tree(tree);
+		mutex_lock(&audit_filter_mutex);
 	}
 	list_del(&cursor);
 	mutex_unlock(&audit_filter_mutex);
_