linux-kernel - Re: [PATCH 2/2] poll: allow f

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Message-ID: <20080826195114.GB19297@infradead.org>
Date:	Tue, 26 Aug 2008 15:51:14 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Tejun Heo <htejun@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Al Viro <viro@...IV.linux.org.uk>, hch@...radead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Van Hensbergen <ericvh@...il.com>,
	Ron Minnich <rminnich@...dia.gov>,
	v9fs-developer@...ts.sourceforge.net, cbe-oss-dev@...abs.org
Subject: Re: [PATCH 2/2] poll: allow f_op->poll to sleep

On Tue, Aug 26, 2008 at 09:58:14AM -0700, Linus Torvalds wrote:
> I don't really see the point.
> 
> poll() isn't allowed to sleep for many reasons. Some are technical. But 
> the most obvious one is that a sleeping "poll()" is totally against the 
> whole point of polling in the first place!
> 
> So is there some big conceptual reason to change how poll() has always 
> worked?

Just as a little sidenote most files on spufs have a ->poll that sleeps,
and currently we don't have any debugging to catch this, I just noticed
this by accident.  The reason that it sleeps is because it needs to grab
a sleping lock, and as that lock protects against a rather complicate
type of hardware context switch it's not possible to replace it with
a spinlock.

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