linux-kernel - Re: [PATCH] Export current_is

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Date:	Tue, 5 Dec 2006 11:31:18 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Andy Fleming <afleming@...escale.com>,
	Ben Collins <ben.collins@...ntu.com>,
	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH] Export current_is_keventd() for libphy

On Tue, 5 Dec 2006 10:07:21 -0800 (PST)
Linus Torvalds <torvalds@...l.org> wrote:

> 
> 
> On Tue, 5 Dec 2006, Maciej W. Rozycki wrote:
> >
> >  One way of avoiding it is calling flush_scheduled_work() from 
> > phy_stop_interrupts().  This is fine as long as a caller of 
> > phy_stop_interrupts() (not necessarily the immediate one calling into 
> > libphy) does not hold the netlink lock.
> > 
> >  If a caller indeed holds the netlink lock, then a driver effectively 
> > calling phy_stop_interrupts() may arrange for the function to be itself 
> > scheduled through the event queue.  This has the effect of avoiding the 
> > race as well, as the queue is processed in order, except it causes more 
> > hassle for the driver.
> 
> I would personally be ok with "flush_scheduled_work()" _itself_ noticing 
> that it is actually waiting to flush "itself", and just being a no-op in 
> that case.

It does do that:

static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
{
	if (cwq->thread == current) {
		/*
		 * Probably keventd trying to flush its own queue. So simply run
		 * it by hand rather than deadlocking.
		 */
		run_workqueue(cwq);

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