linux-kernel - Re: [PATCH] kobject_uevent: add uevent

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Message-ID: <2025040731-eternity-statutory-4a80@gregkh>
Date: Mon, 7 Apr 2025 09:00:35 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: zhoumin <teczm@...mail.com>
Cc: rafael@...nel.org, dakr@...nel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kobject_uevent: add uevent_helper exist check

On Sat, Apr 05, 2025 at 01:31:02AM +0800, zhoumin wrote:
> The kernel creates uevent_helper process for every uevent sent,
> even if the uevent_helper does not exist. Before the rootfs is
> mounted, a large number of events are generated. This change
> introduces uevent_helper existence check to prevent unnecessary
> operations.

What problem is this causing?  What changed to make this actually be a
problem?

> Logs a debug messase before call_usermodehelper_setup.

I can not parse this sentence, sorry.

> e.g.: pr_emerg("action:%s devpath:%s\n", action_string, devpath);
> You will see a large number of uevent_helper processes
> are attempted to be created before the rootfs is mounted.

Again, why is that a problem?

> Signed-off-by: zhoumin <teczm@...mail.com>

Please use your name here, not an alias.

> ---
>  lib/kobject_uevent.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index b7f2fa08d9c8..f3d34ded141a 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -28,6 +28,7 @@
>  #include <net/sock.h>
>  #include <net/netlink.h>
>  #include <net/net_namespace.h>
> +#include <linux/namei.h>
>  
>  
>  atomic64_t uevent_seqnum;
> @@ -58,6 +59,23 @@ static const char *kobject_actions[] = {
>  	[KOBJ_UNBIND] =		"unbind",
>  };
>  
> +#ifdef CONFIG_UEVENT_HELPER
> +static int uevent_helper_lookup(void)
> +{
> +	static int ret = -ENOENT;
> +	struct path path;
> +
> +	if (!ret)
> +		return ret;
> +
> +	ret = kern_path(uevent_helper, LOOKUP_FOLLOW, &path);
> +	if (!ret)
> +		path_put(&path);

What happens when the root filesystem changes to the new one?  This
feels wrong as Andrew said.

thanks,

greg k-h