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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Tejun Heo <tj@kernel.org>
Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Hillf Danton <hdanton@sina.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Marco Elver <elver@google.com>, Zefan Li <lizefan.x@bytedance.com>,
	tglx@linutronix.de
Subject: Re: [PATCH v4 2/6] kernfs: Acquire kernfs_rwsem in
 kernfs_get_parent_dentry().
Message-ID: <20250127084240.yVlHRIoh@linutronix.de>
References: <20250124174614.866884-1-bigeasy@linutronix.de>
 <20250124174614.866884-3-bigeasy@linutronix.de>
 <Z5QeFgyBrxKxE-sg@slm.duckdns.org>
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In-Reply-To: <Z5QeFgyBrxKxE-sg@slm.duckdns.org>

On 2025-01-24 13:11:18 [-1000], Tejun Heo wrote:
> On Fri, Jan 24, 2025 at 06:46:10PM +0100, Sebastian Andrzej Siewior wrote:
> > kernfs_get_parent_dentry() passes kernfs_node::parent to
> > kernfs_get_inode().
> > 
> > Acquire kernfs_root::kernfs_rwsem to ensure kernfs_node::parent isn't
> > replaced during the operation.
> > 
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> This looks fine but wouldn't it be better to use kernfs_rename_lock instead?

iget_locked() has wait_on_inode()/ alloc_inode() so this looks not
compatible with IRQ off.

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

Sebastian