linux-kernel - Re: [PATCH v4 2/6] kernfs: Acquire kernfs_rwsem in kernfs_get_parent

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Message-ID: <20250127084240.yVlHRIoh@linutronix.de>
Date: Mon, 27 Jan 2025 09:42:40 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Tejun Heo <tj@...nel.org>
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 2/6] kernfs: Acquire kernfs_rwsem in
 kernfs_get_parent_dentry().

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@...utronix.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@...nel.org>

Sebastian