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SubjectRe: [PATCH RFC 1/1] module: delay kobject uevent until after module init call
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I tested this on a system that had the script in patch#0 fail 100% of the time.
With this patch, I haven't seen any failure in a few hours.
Haven't seen any unexpected side effect either.

Tested-By: Nicolas Morey-Chaisemartin <nmoreychaisemartin@suse.com>

On 12/3/20 2:51 PM, 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@kernel.org>
> ---
> kernel/module.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index a40ec708f8f2..e1dd0df57244 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1897,7 +1897,6 @@ static int mod_sysfs_init(struct module *mod)
> if (err)
> mod_kobject_put(mod);
>
> - /* delay uevent until full sysfs population */
> out:
> return err;
> }
> @@ -1934,7 +1933,6 @@ static int mod_sysfs_setup(struct module *mod,
> add_sect_attrs(mod, info);
> add_notes_attrs(mod, info);
>
> - kobject_uevent(&mod->mkobj.kobj, KOBJ_ADD);
> return 0;
>
> out_unreg_modinfo_attrs:
> @@ -3656,6 +3654,9 @@ static noinline int do_init_module(struct module *mod)
> blocking_notifier_call_chain(&module_notify_list,
> MODULE_STATE_LIVE, mod);
>
> + /* Delay uevent until module has finished its init routine */
> + kobject_uevent(&mod->mkobj.kobj, KOBJ_ADD);
> +
> /*
> * We need to finish all async code before the module init sequence
> * is done. This has potential to deadlock. For example, a newly
>

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