linux-kernel - Re: [RFC PATCH -v4 07/14] fsnotify: add in inode fsnotify markings

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Date:	Mon, 22 Dec 2008 13:43:00 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Eric Paris <eparis@...hat.com>
Cc:	Evgeniy Polyakov <zbr@...emap.net>, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl, hch@...radead.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk
Subject: Re: [RFC PATCH -v4 07/14] fsnotify: add in inode fsnotify markings

On Sat, Dec 13, 2008 at 11:35:09AM -0500, Eric Paris wrote:

> So to find an entry we need to first grab the inode->i_lock and start to
> walk the inode->i_fsnotify_mark_entries list.  Since we hold the i_lock
> we are not allowed to grab any other locks nor are we allowed to change
> anything other than entry->i_list.  The secret sauce is that we actually
> move the entry from the inode list to a private list which we can walk
> and modify lockless.  Inside the event we actually have to use a
> different list, free_i_list, for this operation so nothing else that
> races with us can mess stuff up.  We run the entire inode we are trying
> to free all entries for an put the entries on the private list.  We do
> NOT modify event->inode.

And just what happens if #3 ("remove entry") hits us in the meanwhile?  Freed
object sitting on free_i_list?
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