From: Steven Rostedt <rostedt@goodmis.org>
To: yu kuai <yukuai3@huawei.com>
Cc: <gregkh@linuxfoundation.org>, <rafael@kernel.org>,
<oleg@redhat.com>, <jack@suse.cz>, <linux-kernel@vger.kernel.org>,
<zhengbin13@huawei.com>, <yi.zhang@huawei.com>,
<chenxiang66@hisilicon.com>, <xiexiuqi@huawei.com>
Subject: Re: [PATCH] debugfs: fix potential infinite loop in debugfs_remove_recursive
Date: Wed, 13 Nov 2019 15:17:55 -0500 [thread overview]
Message-ID: <20191113151755.7125e914@gandalf.local.home> (raw)
In-Reply-To: <1572528884-67565-1-git-send-email-yukuai3@huawei.com>
On Thu, 31 Oct 2019 21:34:44 +0800
yu kuai <yukuai3@huawei.com> wrote:
> debugfs_remove_recursive uses list_empty to judge weather a dentry has
> any subdentry or not. This can lead to infinite loop when any subdir is in
> use.
>
> The problem was discoverd by the following steps in the console.
> 1. use debugfs_create_dir to create a dir and multiple subdirs(insmod);
> 2. cd to the subdir with depth not less than 2;
> 3. call debugfs_remove_recursive(rmmod).
>
> After removing the subdir, the infinite loop is triggered bucause
s/bucause/because/
> debugfs_remove_recursive uses list_empty to judge if the current dir
> doesn't have any subdentry, if so, remove the current dir and which
> will never happen.
>
> Fix the problem by using simple_empty instead of list_empty.
>
> Fixes: 776164c1faac ('debugfs: debugfs_remove_recursive() must not rely on list_empty(d_subdirs)')
> Reported-by: chenxiang66@hisilicon.com
> Signed-off-by: yu kuai <yukuai3@huawei.com>
> ---
> fs/debugfs/inode.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index 7b975db..42b28acc 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -773,8 +773,10 @@ void debugfs_remove_recursive(struct dentry *dentry)
> if (!simple_positive(child))
> continue;
>
> - /* perhaps simple_empty(child) makes more sense */
> - if (!list_empty(&child->d_subdirs)) {
> + /* use simple_empty to prevent infinite loop when any
> + * subdentry of child is in use
> + */
Nit, multi-line comments should be of the form:
/*
* comment line 1
* comment line 2
*/
Not
/* comment line 1
* comment line 2
*/
It's known that the networking folks like that method, but it's not
acceptable anywhere outside of networking.
> + if (!simple_empty(child)) {
Have you tried this with lockdep enabled? I'm thinking that you might
get a splat with holding parent->d_lock and simple_empty(child) taking
the child->d_lock.
-- Steve
> spin_unlock(&parent->d_lock);
> inode_unlock(d_inode(parent));
> parent = child;
next prev parent reply other threads:[~2019-11-13 20:18 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-31 13:34 [PATCH] debugfs: fix potential infinite loop in debugfs_remove_recursive yu kuai
2019-11-13 20:17 ` Steven Rostedt [this message]
2019-11-14 2:01 ` yukuai (C)
2019-11-14 2:43 ` Steven Rostedt
2019-11-14 3:20 ` yukuai (C)
2019-11-14 6:59 ` yukuai (C)
2019-11-14 14:34 ` Steven Rostedt
2019-11-15 1:47 ` yukuai (C)
2019-11-15 1:53 ` Steven Rostedt
2019-11-15 2:13 ` yukuai (C)
2019-11-15 1:57 ` yukuai (C)
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