linux-kernel - Re: [PATCH v4 2/2] livepatch: Add using attribute to klp

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Message-ID: <20240904044807.nnfqlku5hnq5sx3m@treble>
Date: Tue, 3 Sep 2024 21:48:07 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Wardenjohn <zhangwarden@...il.com>
Cc: mbenes@...e.cz, jikos@...nel.org, pmladek@...e.com,
	joe.lawrence@...hat.com, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] livepatch: Add using attribute to klp_func for
 using function show

On Wed, Aug 28, 2024 at 10:23:50AM +0800, Wardenjohn wrote:
> One system may contains more than one livepatch module. We can see
> which patch is enabled. If some patches applied to one system
> modifing the same function, livepatch will use the function enabled
> on top of the function stack. However, we can not excatly know
> which function of which patch is now enabling.
> 
> This patch introduce one sysfs attribute of "using" to klp_func.
> For example, if there are serval patches  make changes to function
> "meminfo_proc_show", the attribute "enabled" of all the patch is 1.
> With this attribute, we can easily know the version enabling belongs
> to which patch.
> 
> The "using" is set as three state. 0 is disabled, it means that this
> version of function is not used. 1 is running, it means that this
> version of function is now running. -1 is unknown, it means that
> this version of function is under transition, some task is still
> chaning their running version of this function.

I'm missing how this is actually useful in the real world.  It feels
like a solution in search of a problem.  And it adds significant
maintenance burden.  Why?

Do you not have any control over what order your patches are applied?
If not, that sounds dangerous and you have much bigger problems.

This "problem" needs to be managed in user space.

-- 
Josh