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

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Message-ID: <20070816115349.GA26908@localdomain>
Date:	Thu, 16 Aug 2007 14:53:50 +0300
From:	Dan Aloni <da-x@...atomic.org>
To:	Oleg Nesterov <oleg@...sign.ru>
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 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.

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).

-- 
Dan Aloni
XIV LTD, http://www.xivstorage.com
da-x (at) monatomic.org, dan (at) xiv.co.il
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