linux-kernel - Re: [PATCH v4 1/6] kernfs: Acquire kernfs_rwsem in kernfs_notify

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Message-ID: <Z5Qdp5iX6Dzkw_ND@slm.duckdns.org>
Date: Fri, 24 Jan 2025 13:09:27 -1000
From: Tejun Heo <tj@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michal Koutný <mkoutny@...e.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hillf Danton <hdanton@...a.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Marco Elver <elver@...gle.com>, Zefan Li <lizefan.x@...edance.com>,
	tglx@...utronix.de
Subject: Re: [PATCH v4 1/6] kernfs: Acquire kernfs_rwsem in
 kernfs_notify_workfn().

Hello,

On Fri, Jan 24, 2025 at 06:46:09PM +0100, Sebastian Andrzej Siewior wrote:
> @@ -911,6 +911,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
>  	/* kick fsnotify */
>  
>  	down_read(&root->kernfs_supers_rwsem);
> +	down_read(&root->kernfs_rwsem);
>  	list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
>  		struct kernfs_node *parent;
>  		struct inode *p_inode = NULL;
> @@ -948,6 +949,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
>  	}
>  
>  	up_read(&root->kernfs_supers_rwsem);
> +	up_read(&root->kernfs_rwsem);
>  	kernfs_put(kn);
>  	goto repeat;

Maybe match the locking and unlocking order so that what's locked last is
unlocked first? Other than that,

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

Thanks.

-- 
tejun