linux-kernel - Re: [PATCH] task_work: remove fifo ordering guarantee

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Message-ID: <20150829125421.GB14973@redhat.com>
Date:	Sat, 29 Aug 2015 14:54:21 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH] task_work: remove fifo ordering guarantee

On 08/29, Ingo Molnar wrote:
>
> So I'm wondering, is there any strong reason why we couldn't use a double linked
> list and still do FIFO and remove that silly linear list walking hack?

This will obviously enlarge callback_head, and it is often embedded.
But this is minor.

If we use a double linked list we can't do task_work_add() lockless.
So we will need another spinlock_t in task_struct. We can't use pi_lock.

Oleg.

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