linux-kernel - Re: ovl: hash non-dir by lower inode for fsnotify

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Date:   Fri, 7 Sep 2018 11:51:32 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     stable <stable@...r.kernel.org>,
        kernel <linux-kernel@...r.kernel.org>,
        Amir Goldstein <amir73il@...il.com>,
        Miklos Szeredi <mszeredi@...hat.com>
Subject: Re: ovl: hash non-dir by lower inode for fsnotify

On Thu, Aug 02, 2018 at 08:29:02AM -0700, Mark Salyzyn wrote:
> On 08/01/2018 11:05 PM, Greg KH wrote:
> > On Wed, Aug 01, 2018 at 02:29:01PM -0700, Mark Salyzyn wrote:
> > > 764baba80168ad3adafb521d2ab483ccbc49e344 ovl: hash non-dir by lower inode
> > > for fsnotify is not part of 4.14 stable and yet it was marked for 4.13
> > > stable merge when committed.
> > > 
> > > Please evaluate.
> > Why not try applying it yourself to 4.14.y and note that it does not
> > apply at all and then provide a working backport so that we can skip at
> > least one email cycle here?  :)
> > 
> > thanks,
> > 
> > greg k-h
> 
> Because I am embarrassed by the backport (!) perhaps? :-)
> 
> +linux-kernel list and authors/approvers for clearance.
> 
> I took some liberty with sb = dentry_d_sb and then sprinkled it in, upstream
> passes sb to the function and the conflicts assumed so.
> 
> --------------------------> snip <-------------------------
> 
> From 764baba80168ad3adafb521d2ab483ccbc49e344 Mon Sep 17 00:00:00 2001
> From: Amir Goldstein <amir73il@...il.com>
> Date: Sun, 4 Feb 2018 15:35:09 +0200
> Subject: ovl: hash non-dir by lower inode for fsnotify
> 
> (cherry pick from commit 764baba80168ad3adafb521d2ab483ccbc49e344)
> 
> Commit 31747eda41ef ("ovl: hash directory inodes for fsnotify")
> fixed an issue of inotify watch on directory that stops getting
> events after dropping dentry caches.
> 
> A similar issue exists for non-dir non-upper files, for example:
> 
> $ mkdir -p lower upper work merged
> $ touch lower/foo
> $ mount -t overlay -o
> lowerdir=lower,workdir=work,upperdir=upper none merged
> $ inotifywait merged/foo &
> $ echo 2 > /proc/sys/vm/drop_caches
> $ cat merged/foo
> 
> inotifywait doesn't get the OPEN event, because ovl_lookup() called
> from 'cat' allocates a new overlay inode and does not reuse the
> watched inode.
> 
> Fix this by hashing non-dir overlay inodes by lower real inode in
> the following cases that were not hashed before this change:
>  - A non-upper overlay mount
>  - A lower non-hardlink when index=off
> 
> A helper ovl_hash_bylower() was added to put all the logic and
> documentation about which real inode an overlay inode is hashed by
> into one place.
> 
> The issue dates back to initial version of overlayfs, but this
> patch depends on ovl_inode code that was introduced in kernel v4.13.
> 
> Signed-off-by: Amir Goldstein <amir73il@...il.com>
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> Cc: <stable@...r.kernel.org> #v4.13
> Signed-off-by: Mark Salyzyn <salyzyn@...roid.com> #v4.14
> ---
>  fs/overlayfs/inode.c | 62 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 44 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 28a320464609a..7cfef4152e9a4 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -14,6 +14,7 @@
>  #include <linux/posix_acl.h>
>  #include <linux/ratelimit.h>
>  #include "overlayfs.h"
> +#include "ovl_entry.h"
> 
>  int ovl_setattr(struct dentry *dentry, struct iattr *attr)
>  {
> @@ -608,39 +609,63 @@ static bool ovl_verify_inode(struct inode *inode,
> struct dentry *lowerdentry,

As this patch is deemed "good", can you please resend it in a
non-corrupted way so that I can apply it to the 4.14.y tree?

thanks,

greg k-h