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

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Message-ID: <20070821060956.GA1778@ff.dom.local>
Date:	Tue, 21 Aug 2007 08:09:56 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Dan Aloni <da-x@...atomic.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Eric W\. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] tty_io.c: don't use flush_scheduled_work()

On Thu, Aug 16, 2007 at 02:53:50PM +0300, 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 

IMHO, it was rather a busy sleep.

> 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.
> 
> A temporary workaround was to give just the workqueue events/* threads a 
> SCHED_FIFO static priority of 99, but I have kept that small patch to 
> myself (figured it's just too nasty).

It looks like there was something more than this one SCHED_RR:
probably some high priority task(s) could have preempted workqueue
thread, delaying run_workqueues. Then it should be an interesting test
for this new, 2.6.23 scheduler.

Regards,
Jarek P.

PS: sorry for so delayed responsing.
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