linux-kernel - Re: [PATCH/RFC 2.6.21 3/5] ehca: completion queue: remove use of do

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Date:	Thu, 11 Jan 2007 13:40:54 -0600
From:	Nathan Lynch <ntl@...ox.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Hoang-Nam Nguyen <hnguyen@...ux.vnet.ibm.com>,
	Roland Dreier <rdreier@...co.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	openfabrics-ewg@...nib.org, openib-general@...nib.org,
	raisch@...ibm.com
Subject: Re: [PATCH/RFC 2.6.21 3/5] ehca: completion queue: remove use of do_mmap()

Christoph Hellwig wrote:
> On Thu, Jan 11, 2007 at 08:08:36PM +0100, Hoang-Nam Nguyen wrote:
> 
> >  	spin_lock_irqsave(&ehca_cq_idr_lock, flags);
> >  	while (my_cq->nr_callbacks)
> >  		yield();
> 
> Calling yield is a very bad idea in general.  You should probably
> add a waitqueue that gets woken when nr_callbacks reaches zero to
> sleep effectively here.

Isn't that code outright buggy?  Calling into the scheduler with a
spinlock held and local interrupts disabled...

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