linux-kernel - Re: [announce] vfs-scale git tree update

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Date:	Tue, 11 Jan 2011 10:13:32 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	aelder@....com, Ian Kent <raven@...maw.net>
Cc:	Nick Piggin <npiggin@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [announce] vfs-scale git tree update

[ Added Ian to cc - the BUG_ON() in d_set_d_op() triggers on autofs4,
see lkml thread for more details if you care ]

On Tue, Jan 11, 2011 at 9:57 AM, Alex Elder <aelder@....com> wrote:
>
> Looking at it quickly, I don't think that would matter for
> the case at hand.  I.e., that might be safer but it doesn't
> address the fact that these fields are getting initialized
> multiple times.

You're right - without looking closer or thinking about it any more, I
was thinking mkdir etc would create the new dentry, but it can easily
be a pre-existing negative one. So it's not like mkdir is always going
to be something new that can just be initialized.

So yeah, no race or anything like that required - just regular acceses.

That said, if we make sure that the d_op gets cleared (or the dentry
dropped) when something turns negative, and a negative lookup never
sets d_op, it should all basically work.

Can you figure out the exact sequence that causes this? Is it enough
to just mount something once?

                 Linus
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