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Date: Tue, 5 Dec 2023 12:14:29 +0100
From: Christian Brauner <brauner@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: NeilBrown <neilb@suse.de>, Al Viro <viro@zeniv.linux.org.uk>,
	Oleg Nesterov <oleg@redhat.com>,
	Chuck Lever <chuck.lever@oracle.com>,
	Jeff Layton <jlayton@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nfs@vger.kernel.org
Subject: Re: [PATCH 1/2] Allow a kthread to declare that it calls
 task_work_run()
Message-ID: <20231205-altbacken-umbesetzen-e5c0c021ab98@brauner>
References: <20231204014042.6754-1-neilb@suse.de>
 <20231204014042.6754-2-neilb@suse.de>
 <e9a1cfed-42e9-4174-bbb3-1a3680cf6a5c@kernel.dk>
 <170172377302.7109.11739406555273171485@noble.neil.brown.name>
 <a070b6bd-0092-405e-99d2-00002596c0bc@kernel.dk>
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In-Reply-To: <a070b6bd-0092-405e-99d2-00002596c0bc@kernel.dk>

On Mon, Dec 04, 2023 at 03:09:44PM -0700, Jens Axboe wrote:
> 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,

Yeah, I'm not too fond of that part as well. I don't think we want to
give modules the ability to mess with task work. This is just asking for
trouble.