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

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Message-ID: <20150831124442.GB31015@redhat.com>
Date:	Mon, 31 Aug 2015 14:44:42 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>,
	Ingo Molnar <mingo@...nel.org>,
	Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH] task_work: remove fifo ordering guarantee

On 08/29, Linus Torvalds wrote:
>
> On Sat, Aug 29, 2015 at 7:11 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> > If this needs to be kept, maybe then add following, to make sure
> > we flush the list at most every BITS_PER_LONG files
>
> Hmm.
>
> I'm wondering if we should just make close_files() (or maybe even
> filp_close()) use a synchronous fput().

Heh. I thought about the same change. So perhaps it is even the right
thing to do. Still I am worried, because "it can't be that simple" ;)

And, with this change close_files() is called before exit_fs() and
exit_task_namespaces(). This is fine (iiuc), but this means that the
creative code in drivers/ can (wrongly) rely on this fact again. IIRC,
the change which moved __fput() into task_work_exit() uncovered some
interesting problems, like filp_open() called from fop->release().

Anyway, this is the question to Al, I guess.

Oleg.

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