fix d_walk()/non-delayed __d_free() race

I checked Jari's explanation below and found that v3.14.77 and v3.12.62
are missing the same fix as 3.10. In fact Al's original commit 3d56c25e
("fix d_walk()/non-delayed __d_free() race") used to mention to check 
this __d_materialise_dentry() function in the Cc: stable line, but this
got lost during the backports.

Normally all of our 3 kernels need to apply the following patch that
Ben correctly put in 3.16 and 3.2. I'm fixing the backport in 3.10.103
right now.

On Mon, Aug 22, 2016 at 04:56:57PM +0300, Jari Ruusu wrote:
> This patch for 3.10 branch appears to be missing one important
> 
> +       dentry->d_flags |= DCACHE_RCUACCESS;
> 
> in fs/dcache.c __d_materialise_dentry() function. When Ben Hutchings
> backported Al Viro's original fix to stable branches that he maintains,
> he added that one additional line to both 3.2 and 3.16 branches. Please
> consider including that additional one line fix for 3.10 stable branch
> also.
> 
> 
> Ben Hutchings said this on his 3.2.82-rc1 patch:
> [bwh: Backported to 3.2:
>  - Adjust context
>  - Also set the flag in __d_materialise_dentry())]
> 
> http://marc.info/?l=linux-kernel&m=147117565612275&w=2
> 
> 
> Ben Hutchings said this on his 3.16.37-rc1 patch:
> [bwh: Backported to 3.16:
>  - Adjust context
>  - Also set the flag in __d_materialise_dentry())]
> 
> http://marc.info/?l=linux-kernel&m=147117433412006&w=2
> 
> 
> Also mentioned by Sasha Levin on 3.18 and 4.1 commits:
> Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry())
> 
> http://marc.info/?l=linux-stable-commits&m=146648034410827&w=2
> http://marc.info/?l=linux-stable-commits&m=146647471009771&w=2Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/dcache.c

@@ -2652,6 +2652,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon)
 	switch_names(dentry, anon);
 	swap(dentry->d_name.hash, anon->d_name.hash);
 
+	dentry->d_flags |= DCACHE_RCUACCESS;
 	dentry->d_parent = dentry;
 	list_del_init(&dentry->d_child);
 	anon->d_parent = dparent;