linux-kernel - Re: [systemd-devel] [PATCH RFC 1/1] module: delay kobject uevent until after module init call

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Date:   Thu, 3 Dec 2020 19:32:19 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     linux-kernel@...r.kernel.org, systemd-devel@...ts.freedesktop.org,
        Franck Bui <fbui@...e.com>,
        Nicolas Morey-Chaisemartin <nmoreychaisemartin@...e.com>
Subject: Re: [systemd-devel] [PATCH RFC 1/1] module: delay kobject uevent
 until after module init call

On Thu, Dec 03, 2020 at 02:51:24PM +0100, Jessica Yu wrote:
> Apparently there has been a longstanding race between udev/systemd and
> the module loader. Currently, the module loader sends a uevent right
> after sysfs initialization, but before the module calls its init
> function. However, some udev rules expect that the module has
> initialized already upon receiving the uevent.
> 
> This race has been triggered recently (see link in references) in some
> systemd mount unit files. For instance, the configfs module creates the
> /sys/kernel/config mount point in its init function, however the module
> loader issues the uevent before this happens. sys-kernel-config.mount
> expects to be able to mount /sys/kernel/config upon receipt of the
> module loading uevent, but if the configfs module has not called its
> init function yet, then this directory will not exist and the mount unit
> fails. A similar situation exists for sys-fs-fuse-connections.mount, as
> the fuse sysfs mount point is created during the fuse module's init
> function. If udev is faster than module initialization then the mount
> unit would fail in a similar fashion.
> 
> To fix this race, delay the module KOBJ_ADD uevent until after the
> module has finished calling its init routine.
> 
> References: https://github.com/systemd/systemd/issues/17586
> Signed-off-by: Jessica Yu <jeyu@...nel.org>

Nice fix:
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>