linux-kernel - Re: Warn people about flush_scheduled

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Message-ID: <Pine.LNX.4.44L0.0912141803000.2690-100000@iolanthe.rowland.org>
Date:	Mon, 14 Dec 2009 18:04:51 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Tejun Heo <tj@...nel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Warn people about flush_scheduled_work()

On Mon, 14 Dec 2009, Oliver Neukum wrote:

> Am Montag, 14. Dezember 2009 23:02:51 schrieb Alan Stern:
> > On Mon, 14 Dec 2009, Oliver Neukum wrote:
> > 
> > > Am Montag, 14. Dezember 2009 22:33:38 schrieb Alan Stern:
> > > >         Consider using cancel_work_sync() or cancel_delayed_work_sync()
> > > >         instead.  In most situations they will accomplish what you 
> > > >         need.
> > > 
> > > In which respect is cancel_work_sync() fundamentally safer?
> > > If the work is already running and takes a lock you are holding,
> > > then what?
> > 
> > With cancel_work_sync() you know what locks the work item is going to
> > take, since it's your work item.  With flush_scheduled_work() you have
> > no idea what locks will be needed by the items on the queue.  They 
> > could come from anywhere.
> 
> True, but what use is that if you don't know your call chain and the locks
> it takes.

Okay, clearly you have to know something about your call chain.  The
comment should be toned down a little bit.

Alan Stern

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