linux-kernel - Re: [PATCH 1/2] Allow a kthread to declare that it calls task_work

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Message-ID: <a070b6bd-0092-405e-99d2-00002596c0bc@kernel.dk>
Date:   Mon, 4 Dec 2023 15:09:44 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     NeilBrown <neilb@...e.de>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        Jeff Layton <jlayton@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org
Subject: Re: [PATCH 1/2] Allow a kthread to declare that it calls
 task_work_run()

On 12/4/23 2:02 PM, NeilBrown wrote:
> It isn't clear to me what _GPL is appropriate, but maybe the rules
> changed since last I looked..... are there rules?
> 
> My reasoning was that the call is effectively part of the user-space
> ABI.  A user-space process can call this trivially by invoking any
> system call.  The user-space ABI is explicitly a boundary which the GPL
> does not cross.  So it doesn't seem appropriate to prevent non-GPL
> kernel code from doing something that non-GPL user-space code can
> trivially do.

By that reasoning, basically everything in the kernel should be non-GPL
marked. And while task_work can get used by the application, it happens
only indirectly or implicitly. So I don't think this reasoning is sound
at all, it's not an exported ABI or API by itself.

For me, the more core of an export it is, the stronger the reason it
should be GPL. FWIW, I don't think exporting task_work functionality is
a good idea in the first place, but if there's a strong reason to do so,
it should most certainly not be accessible to non-GPL modules. Basically
NO new export should be non-GPL.

-- 
Jens Axboe