Re: 2.6.24-rc3-git4 NFS crossmnt regression

[ebiederm@xmission.com (Eric W. Biederman)]

Andrew Morton <akpm@linux-foundation.org> writes:

> On Fri, 07 Dec 2007 17:51:58 -0500
> Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
>
>> 
>> On Fri, 2007-12-07 at 14:39 -0500, Shane wrote:
>> > On Dec 7, 2007 2:16 PM, Shane <gnome42@gmail.com> wrote:
>> > ...
>> > > Confirmed working in rc4-git5.  I'll deploy this kernel in a few more
>> > > spots and check for other regressions.
>> > 
>> > Hmm, I installed a new kernel built from the same sources on the NFS
>> > server. And now I don't see anything at all in the crossmnt dirs.
>> > 
>> > ls /dirA/dirB/dirC  --> zero output (empty dir)
>> > 
>> > Are there any other pending fixes?
>> > 
>> > Shane
>> 
>> You've probably fallen afoul of 
>> 
>>    http://bugzilla.kernel.org/show_bug.cgi?id=9504
>> 
>
> Yeah.
>
> I have a tentative fix below but I can't seem to get Eric and Denis to get
> a suitable fix nailed down.  It's urgent!

Andrew, if it is truly urgent please grab either fix, as they will sort
out the worst of the symptoms.

Mine is a little more thorough, and possibly a little less performant.
However since mounts don't appear to be residing under /proc/net it
isn't a significant issue.

> From: "Denis V. Lunev" <den@openvz.org>
>
> /proc/sys/fs/binfmt_misc dentry disappeared during d_revalidate. 
> d_revalidate only dentries from shadowed one and below. 
> http://bugzilla.kernel.org/show_bug.cgi?id=9504
>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Marcus Better <marcus@better.se>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Cc: Marcus Better <marcus@better.se>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>  fs/proc/generic.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff -puN fs/proc/generic.c~lost-content-of-proc-sys-fs-binfmt_misc
> fs/proc/generic.c
> --- a/fs/proc/generic.c~lost-content-of-proc-sys-fs-binfmt_misc
> +++ a/fs/proc/generic.c
> @@ -380,12 +380,17 @@ static int proc_revalidate_dentry(struct
>  	return 0;
>  }
>  
> -static struct dentry_operations proc_dentry_operations =
> +static struct dentry_operations proc_dentry_shadow_operations =
>  {
>  	.d_delete	= proc_delete_dentry,
>  	.d_revalidate	= proc_revalidate_dentry,
>  };
>  
> +static struct dentry_operations proc_dentry_operations =
> +{
> +	.d_delete	= proc_delete_dentry,
> +};
> +
>  /*
>   * Don't create negative dentries here, return -ENOENT by hand
>   * instead.
> @@ -394,6 +399,7 @@ struct dentry *proc_lookup(struct inode 
>  {
>  	struct inode *inode = NULL;
>  	struct proc_dir_entry * de;
> +	int use_shadow = 0;
>  	int error = -ENOENT;
>  
>  	lock_kernel();
> @@ -406,8 +412,10 @@ struct dentry *proc_lookup(struct inode 
>  			if (!memcmp(dentry->d_name.name, de->name, de->namelen))
> {
>  				unsigned int ino;
>  
> -				if (de->shadow_proc)
> +				if (de->shadow_proc) {
>  					de = de->shadow_proc(current, de);
> +					use_shadow = 1;
> +				}
>  				ino = de->low_ino;
>  				de_get(de);
>  				spin_unlock(&proc_subdir_lock);
> @@ -423,6 +431,8 @@ struct dentry *proc_lookup(struct inode 
>  
>  	if (inode) {
>  		dentry->d_op = &proc_dentry_operations;
> +		dentry->d_op = use_shadow ?
> + &proc_dentry_shadow_operations : dentry->d_parent->d_op;
>  		d_add(dentry, inode);
>  		return NULL;
>  	}
> _