linux-kernel - Re: [PATCH RESEND] klist: don't iterate over deleted entries

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Date:	Mon, 25 Aug 2008 12:21:30 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tejun Heo <teheo@...e.de>
cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] klist: don't iterate over deleted entries

On Mon, 25 Aug 2008, Tejun Heo wrote:

> A klist entry is kept on the list till all its current iterations are
> finished; however, a new iteration after deletion also iterates over
> deleted entries as long as their reference count stays above zero.
> This causes problems for cases where there are users which iterate
> over the list while synchronized against list manipulations and
> natuarally expect already deleted entries to not show up during
> iteration.
> 
> This patch implements dead flag which gets set on deletion so that
> iteration can skip already deleted entries.  The dead flag piggy backs
> on the lowest bit of knode->n_klist and only visible to klist
> implementation proper.

This seems like a reasonable sort of thing to do.  I had considered 
something like it in the past, but never bothered because it wasn't 
needed at the time.

Alan Stern

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