linux-kernel - [RFC PATCH 0/1] task_work_queue: add generic process-context callbacks

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Date:	Tue, 10 Apr 2012 03:05:47 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, David Smith <dsmith@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>
Subject: [RFC PATCH 0/1] task_work_queue: add generic process-context
	callbacks

Hello.

I didn't read the "v3.4-rc2 out-of-memory problems" thread yet, but
I noticed how much Linus loves the
yet-another-random-notifier-for-some-random-reason idea.

Yet I am going to suggest another one, please see the patch.

But. To defence this change, please note that de-facto the notifier
is already here.

On 04/09, Oleg Nesterov wrote:
>
> Note: initially this was 1/2. The usage of >replacement_session_keyring
> is racy, although the problem is minor. I think that instead of fixing
> a lot of key_replace_session_keyring's callers in arch/ we can add the
> simple abstraction layer and kill ->replacement_session_keyring. I'll
> try to send the patches tomorrow.

Yes. the callers of key_replace_session_keyring() and
keyctl_session_to_parent() lack the barriers and can race with each other.
And keyctl_session_to_parent() probably needs kick_process(). Yes, the
problem is minor, but still.

To me, the main problem is task->->replacement_session_keyring itself.
I mean, imho it should not be that limited, we should generalize this
logic.

And potentially (I hope) it can have more users besides
KEYCTL_SESSION_TO_PARENT. Say, we can remove do_exit()->exit_irq_thread()
and task->irq_thread. The creator of irq thread can do
task_queue_work(exit_irq_thread).

What do you think?

Oleg.

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