linux-kernel - Re: vfs-scale, d_revalidate from nfsd

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Message-ID: <AANLkTik1bj=Z9xFv8JfYrxqefFL1owmH=Rctj=XnH4Mp@mail.gmail.com>
Date:	Fri, 14 Jan 2011 13:57:55 +1100
From:	Nick Piggin <npiggin@...il.com>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
Cc:	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: vfs-scale, d_revalidate from nfsd

On Fri, Jan 14, 2011 at 1:03 AM, J. R. Okajima <hooanon05@...oo.co.jp> wrote:
>
> NFSD calls filesystem's ->d_revalidate() with the parameter nd == NULL.
> So every
>        if (nd->flags & LOOKUP_RCU)
>                return -ECHILD;
> code which was added to ->d_revalidate() of FS which supports NFS
> exporting will crash.
>
> If we rewrite it as
>        if (nd && (nd->flags & LOOKUP_RCU))
>                return -ECHILD;
> the problem may not occur.
> But I am not sure whether lookup_one_len() call in NFSD support rcu-walk.

Ah, good catch.

I'm going to change the d_revalidate API so it takes and inode and rcu-walk
flag parameter to make it easier for filesystems to implement rcu-walk.

That will take care of this NULL nd case.

Thanks,
Nick
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