linux-kernel - Re: [PATCH] fs/kernfs: Fix lockdep warning in kernfs

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Message-ID: <Y2vLXWvZ9uwaVICx@slm.duckdns.org>
Date:   Wed, 9 Nov 2022 05:46:37 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        syzbot+2fdf66e68f5f882c1074@...kaller.appspotmail.com
Subject: Re: [PATCH] fs/kernfs: Fix lockdep warning in kernfs_active()

On Wed, Nov 09, 2022 at 08:04:15PM +0800, Chengming Zhou wrote:
> syzbot found a lockdep warning in kernfs_find_and_get_node_by_id(),
> bisected to the commit c25491747b21 ("kernfs: Add KERNFS_REMOVING flags"),
> which didn't hold kernfs_rwsem before call kernfs_active(kn).
> 
> Since kernfs_find_and_get_node_by_id() doesn't have to get active count
> of kn, only need to get a stable refcount of kn, so it should be enough
> to just check kn has been KERNFS_ACTIVATED.
> 
> Reported-by: syzbot+2fdf66e68f5f882c1074@...kaller.appspotmail.com
> Fixes: c25491747b21 ("kernfs: Add KERNFS_REMOVING flags")
> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun