linux-kernel - Re: [PATCH 3/3] tty_io.c: don't use flush_scheduled

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Date:	Thu, 16 Aug 2007 20:03:09 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Dan Aloni <da-x@...atomic.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>, Jarek Poplawski <jarkao2@...pl>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] tty_io.c: don't use flush_scheduled_work()

On 08/16, Dan Aloni wrote:
>
> On Sun, Jul 01, 2007 at 07:37:49PM +0400, Oleg Nesterov wrote:
> > I don't know how to test this patch, the ack/nack from maintainer is wanted.
> > 
> > flush_scheduled_work() is evil and should be avoided. Change tty_set_ldisc()
> > and release_dev() to use cancel_delayed_work_sync/cancel_work_sync.
> > 
> > I am not sure we really need to call do_tty_hangup() when cancel_work_sync()
> > returns true, but this matches the current behaviour.
> 
> I also noticed this problem recently with 2.6.22, on a 2-CPU box where there 
> was one SCHED_RR userspace process stuck in a busy loop. The box was completely 
> responsive but had this annoyance where all tty closings were stuck in 
> flush_scheduled_work(). It's especially noticable when you ssh to the machine
> and then try to log out.

cancel_work_sync(work) can hang too if some SCHED_RR userspace process does not
relinquish CPU, but the probability is much lower (it should preempt work->func
of that work_struct).

see also http://marc.info/?l=linux-kernel&m=118115098120503.

Oleg.

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