linux-kernel - Re: [PATCH V3 07/21] dax: prevent driver unbind while filesystem holds device

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Message-ID: <fcik72d66pfzk4xvubywt2mzdqr4lqtqjgexrqr3l3acpxc5hv@vp6oueyvzrll>
Date: Mon, 12 Jan 2026 12:55:49 -0600
From: John Groves <John@...ves.net>
To: Miklos Szeredi <miklos@...redi.hu>, 
	Dan Williams <dan.j.williams@...el.com>, Bernd Schubert <bschubert@....com>, 
	Alison Schofield <alison.schofield@...el.com>
Cc: John Groves <jgroves@...ron.com>, Jonathan Corbet <corbet@....net>, 
	Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, 
	Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>, 
	Alexander Viro <viro@...iv.linux.org.uk>, David Hildenbrand <david@...nel.org>, 
	Christian Brauner <brauner@...nel.org>, "Darrick J . Wong" <djwong@...nel.org>, 
	Randy Dunlap <rdunlap@...radead.org>, Jeff Layton <jlayton@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
	Stefan Hajnoczi <shajnocz@...hat.com>, Joanne Koong <joannelkoong@...il.com>, 
	Josef Bacik <josef@...icpanda.com>, Bagas Sanjaya <bagasdotme@...il.com>, 
	Chen Linxuan <chenlinxuan@...ontech.com>, James Morse <james.morse@....com>, Fuad Tabba <tabba@...gle.com>, 
	Sean Christopherson <seanjc@...gle.com>, Shivank Garg <shivankg@....com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Gregory Price <gourry@...rry.net>, 
	Aravind Ramesh <arramesh@...ron.com>, Ajay Joshi <ajayjoshi@...ron.com>, venkataravis@...ron.com, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, 
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V3 07/21] dax: prevent driver unbind while filesystem
 holds device

On 26/01/07 09:33AM, John Groves wrote:
> From: John Groves <John@...ves.net>
> 
> Add custom bind/unbind sysfs attributes for the dax bus that check
> whether a filesystem has registered as a holder (via fs_dax_get())
> before allowing driver unbind.
> 
> When a filesystem like famfs mounts on a dax device, it registers
> itself as the holder via dax_holder_ops. Previously, there was no
> mechanism to prevent driver unbind while the filesystem was mounted,
> which could cause some havoc.
> 
> The new unbind_store() checks dax_holder() and returns -EBUSY if
> a holder is registered, giving userspace proper feedback that the
> device is in use.
> 
> To use our custom bind/unbind handlers instead of the default ones,
> set suppress_bind_attrs=true on all dax drivers during registration.
> 
> Signed-off-by: John Groves <john@...ves.net>

After a discussion with Dan Williams, I will be dropping this patch
from the series. If the fsdev-mode driver gets unbound under famfs,
famfs will just stop working.

Based on feedback so far, V4 should be coming in the next few days.

Regards,
John