linux-kernel - Re: [RFC PATCH] kobject: fix uevent helper execution order issues

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Message-ID: <2025081956-untie-elude-7880@gregkh>
Date: Tue, 19 Aug 2025 20:29:12 +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: [RFC PATCH] kobject: fix uevent helper execution order issues

On Wed, Aug 20, 2025 at 01:18:28AM +0800, zhoumin wrote:
> The current use of the UMH_NO_WAIT parameter does not guarantee the
> sequential execution of CONFIG_STATIC_USERMODEHELPER_PATH.

There is never any such guarantee.  Unless you are on a single processor
system.

> For example, when fdisk completes and issues a BLKRRPART ioctl command,
> kernel first sending remove events followed by an add events. However, 
> process CONFIG_STATIC_USERMODEHELPER_PATH may execute
> out-of-order—potentially handling the add before the remove. This can
> result in the new partition being unexpectedly unmounted instead of mounted
> as intended.

Why are you not looking at the SEQNUM value?  That should be what orders
the events, right?  Otherwise how would any of this work?  :)

Also, what usermode helper program are you using that requires a binary?
What is wrong with udev?

thanks,

greg k-h