linux-kernel - Re: [PATCH] cifs - check S

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Message-ID: <CA+55aFwx-vCQcbU5pKcRxFm1uJmjrT_OafTTMx026idX+H1oJg@mail.gmail.com>
Date:	Fri, 27 Apr 2012 19:46:01 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steve French <smfrench@...il.com>
Cc:	Ian Kent <raven@...maw.net>, Jeff Layton <jlayton@...hat.com>,
	linux-cifs@...r.kernel.org,
	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cifs - check S_AUTOMOUNT in revalidate

Steve? I have a CIFS pull request from you now, and it doesn't contain
this one. I don't know the code well enough to say one way or the
other, so I haven't applied this. Pls Ack/Nak.

                   Linus

On Fri, Apr 27, 2012 at 1:18 AM, Ian Kent <raven@...maw.net> wrote:
> When revalidating a dentry, if the inode wasn't known to be a dfs
> entry when the dentry was instantiated, such as when created via
> ->readdir(), the DCACHE_NEED_AUTOMOUNT flag needs to be set on the
> dentry in ->d_revalidate().
>
> The false return from cifs_d_revalidate(), due to the inode now
> being marked with the S_AUTOMOUNT flag, might not invalidate the
> dentry if there is a concurrent unlazy path walk. This is because
> the dentry reference count will be at least 2 in this case causing
> d_invalidate() to return EBUSY. So the asumption that the dentry
> will be discarded then correctly instantiated via ->lookup() might
> not hold.
>
> Signed-off-by: Ian Kent <raven@...maw.net>
> Reviewed-by: Jeff Layton <jlayton@...hat.com>
> Cc: Steve French <smfrench@...il.com>
> Cc: linux-cifs@...r.kernel.org
> ---
>
>  fs/cifs/dir.c |   17 ++++++++++++-----
>  1 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
> index d172c8e..ec4e9a2 100644
> --- a/fs/cifs/dir.c
> +++ b/fs/cifs/dir.c
> @@ -668,12 +668,19 @@ cifs_d_revalidate(struct dentry *direntry, struct nameidata *nd)
>                        return 0;
>                else {
>                        /*
> -                        * Forcibly invalidate automounting directory inodes
> -                        * (remote DFS directories) so to have them
> -                        * instantiated again for automount
> +                        * If the inode wasn't known to be a dfs entry when
> +                        * the dentry was instantiated, such as when created
> +                        * via ->readdir(), it needs to be set now since the
> +                        * attributes will have been updated by
> +                        * cifs_revalidate_dentry().
>                         */
> -                       if (IS_AUTOMOUNT(direntry->d_inode))
> -                               return 0;
> +                       if (IS_AUTOMOUNT(direntry->d_inode) &&
> +                          !(direntry->d_flags & DCACHE_NEED_AUTOMOUNT)) {
> +                               spin_lock(&direntry->d_lock);
> +                               direntry->d_flags |= DCACHE_NEED_AUTOMOUNT;
> +                               spin_unlock(&direntry->d_lock);
> +                       }
> +
>                        return 1;
>                }
>        }
>
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