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

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Message-ID: <20201210123900.GA28117@linux-8ccs>
Date:   Thu, 10 Dec 2020 13:39:00 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     linux-kernel@...r.kernel.org, systemd-devel@...ts.freedesktop.org
Cc:     Nicolas Morey-Chaisemartin <nmoreychaisemartin@...e.com>,
        Franck Bui <fbui@...e.com>
Subject: Re: [PATCH RFC 1/1] module: delay kobject uevent until after module
 init call

+++ Jessica Yu [03/12/20 14:51 +0100]:
>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>

Thanks all, this has been applied to modules-next to try to get as
much -next time as possible before the upcoming merge window.

Jessica