linux-kernel - Re: [PATCH 2.6.24-rc4] proc: Remove/Fix proc generic d

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Date:	Sat, 8 Dec 2007 12:15:44 -0500
From:	Shane <gnome42@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Alexey Dobriyan" <adobriyan@...il.com>, rjw@...k.pl,
	trond.myklebust@....uio.no, linux-kernel@...r.kernel.org,
	bfields@...ldses.org, den@...nvz.org,
	"Pavel Emelyanov" <xemul@...nvz.org>
Subject: Re: [PATCH 2.6.24-rc4] proc: Remove/Fix proc generic d_revalidate

On Dec 7, 2007 11:25 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> Ultimately to implement /proc perfectly we need an implementation
> of d_revalidate because files and directories can be removed behind
> the back of the VFS, and d_revalidate is the only way we can let
> the VFS know that this has happened.
>
> Unfortunately the linux VFS can not cope with anything in the path
> to a mount point going away.  So a proper d_revalidate method that
> calls d_drop also needs to call have_submounts which is moderately
> expensive, so you really don't want a d_revalidate method that
> unconditionally calls it, but instead only calls it when the
> backing object has really gone away.
>
> proc generic entries only disappear on module_unload (when
> not counting the fledgling network namespace) so it is quite rare
> that we actually encounter that case and has not actually caused
> us real world trouble yet.
>
> So until we get a proper test for keeping dentries in the dcache
> fix the current d_revalidate method by completely removing it.  This
> returns us to the current status quo.
>
> So with CONFIG_NETNS=n things should look as they have always looked.
>
> For CONFIG_NETNS=y things work most of the time but there are a few
> rare corner cases that don't behave properly.  As the network namespace
> is barely present in 2.6.24 this should not be a problem.
>
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> ---
>  fs/proc/generic.c |    7 -------
>  1 files changed, 0 insertions(+), 7 deletions(-)
>
> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> index 8d49838..6a2fe51 100644
> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -374,16 +374,9 @@ static int proc_delete_dentry(struct dentry * dentry)
>         return 1;
>  }
>
> -static int proc_revalidate_dentry(struct dentry *dentry, struct nameidata *nd)
> -{
> -       d_drop(dentry);
> -       return 0;
> -}
> -
>  static struct dentry_operations proc_dentry_operations =
>  {
>         .d_delete       = proc_delete_dentry,
> -       .d_revalidate   = proc_revalidate_dentry,
>  };
>
>  /*
> --
> 1.5.3.rc6.17.g1911

Confirmed. This patch fixes the problem for me.

Shane
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