linux-kernel - Re: [PATCH] Export current_is

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Date:	Wed, 6 Dec 2006 15:25:22 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Andrew Morton <akpm@...l.org>
cc:	Roland Dreier <rdreier@...co.com>,
	Andy Fleming <afleming@...escale.com>,
	Ben Collins <ben.collins@...ntu.com>,
	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH] Export current_is_keventd() for libphy

On Tue, 5 Dec 2006, Andrew Morton wrote:

> But running flush_scheduled_work() from within dev_close() is a very
> sensible thing to do, and dev_close is called under rtnl_lock().
> davem is -> thattaway ;)

 And when within dev_close() there is quite a chance there is 
linkwatch_event() somewhere in the event queue already. ;-)

> Ah.  The point is that the phy code doesn't want to flush _all_ pending
> callbacks.  It only wants to flush its own one.  And its own one doesn't
> take rtnl_lock().
> 
> IOW, the phy code has no interest in running some random other subsystem's
> callback - it just wants to run its own.  Hence no deadlock.

 Both are true.  It's linkwatch_event() that's somewhere in the queue 
already that makes the trouble here.

> Maybe the lesson here is that flush_scheduled_work() is a bad function.
> It should really be flush_this_work(struct work_struct *w).  That is in
> fact what approximately 100% of the flush_scheduled_work() callers actually
> want to do.

 There may be cases where flush_scheduled_work() is indeed needed, but 
likely outside drivers, and I agree such a specific call would be useful 
and work here.

  Maciej
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