linux-kernel - Re: [PATCH] fs: don't remove inotify watchers from alive inode-s

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Date:	Mon, 8 Sep 2014 16:45:15 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>,
	Eric Paris <eparis@...isplace.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] fs: don't remove inotify watchers from alive inode-s

On Mon 08-09-14 16:01:56, Andrey Vagin wrote:
> Currently watchers are removed in dentry_iput(), if n_link is zero.
> But other detries can be linked with this inode. For example if we
> create two hard links, open the first one and set a watcher on the
> second one. Then if we remove both links, the watcher will be removed.
> But we will have the alive file descriptor, which allows us to generate
> more events.
> 
> With this patch, watchers will be removed, only if nlink is zero and
> i_dentry list is empty.
> 
> Look at a following example:
> 
> 	fd = inotify_init1(IN_NONBLOCK);
> 	deleted = open(path, O_CREAT | O_TRUNC | O_WRONLY, 0666);
> 	link(path, path_link);
> 
> 	wd_deleted = inotify_add_watch(fd, path_link, IN_ALL_EVENTS);
> 
> 	unlink(path);
> 	unlink(path_link);
> 
> 	printf(" --- unlink\n");
> 	read_evetns(fd);
> 
> 	close(deleted);
> 	printf(" --- close\n");
> 	read_evetns(fd);
> 
> Without this patch:
>  --- unlink
> 4	(IN_ATTRIB)
> 400	(IN_DELETE_SELF)
> 8000	(IN_IGNORED)
>  --- close
> FAIL
> 
> With this patch:
>  --- unlink
> 4	(IN_ATTRIB)
> 400	(IN_DELETE_SELF)
>  --- close
> 8	(IN_CLOSE_WRITE)
> 400	(IN_DELETE_SELF)
> 8000	(IN_IGNORED)
> PASS
> 
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: John McCutchan <john@...nmccutchan.com>
> Cc: Robert Love <rlove@...ve.org>
> Cc: Eric Paris <eparis@...isplace.org>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Signed-off-by: Andrey Vagin <avagin@...nvz.org>
  OK, looks good to me. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/dcache.c              | 10 ++++++++--
>  include/linux/fsnotify.h |  5 +++--
>  2 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index d30ce69..fb1ee58 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -279,13 +279,16 @@ static void dentry_iput(struct dentry * dentry)
>  	__releases(dentry->d_inode->i_lock)
>  {
>  	struct inode *inode = dentry->d_inode;
> +	bool last_dentry;
> +
>  	if (inode) {
>  		dentry->d_inode = NULL;
>  		hlist_del_init(&dentry->d_alias);
> +		last_dentry = hlist_empty(&inode->i_dentry);
>  		spin_unlock(&dentry->d_lock);
>  		spin_unlock(&inode->i_lock);
>  		if (!inode->i_nlink)
> -			fsnotify_inoderemove(inode);
> +			fsnotify_inoderemove(inode, last_dentry);
>  		if (dentry->d_op && dentry->d_op->d_iput)
>  			dentry->d_op->d_iput(dentry, inode);
>  		else
> @@ -304,14 +307,17 @@ static void dentry_unlink_inode(struct dentry * dentry)
>  	__releases(dentry->d_inode->i_lock)
>  {
>  	struct inode *inode = dentry->d_inode;
> +	bool last_dentry;
> +
>  	__d_clear_type(dentry);
>  	dentry->d_inode = NULL;
>  	hlist_del_init(&dentry->d_alias);
>  	dentry_rcuwalk_barrier(dentry);
> +	last_dentry = hlist_empty(&inode->i_dentry);
>  	spin_unlock(&dentry->d_lock);
>  	spin_unlock(&inode->i_lock);
>  	if (!inode->i_nlink)
> -		fsnotify_inoderemove(inode);
> +		fsnotify_inoderemove(inode, last_dentry);
>  	if (dentry->d_op && dentry->d_op->d_iput)
>  		dentry->d_op->d_iput(dentry, inode);
>  	else
> diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
> index 1c804b0..63dae9d 100644
> --- a/include/linux/fsnotify.h
> +++ b/include/linux/fsnotify.h
> @@ -144,10 +144,11 @@ static inline void fsnotify_nameremove(struct dentry *dentry, int isdir)
>  /*
>   * fsnotify_inoderemove - an inode is going away
>   */
> -static inline void fsnotify_inoderemove(struct inode *inode)
> +static inline void fsnotify_inoderemove(struct inode *inode, bool delete)
>  {
>  	fsnotify(inode, FS_DELETE_SELF, inode, FSNOTIFY_EVENT_INODE, NULL, 0);
> -	__fsnotify_inode_delete(inode);
> +	if (delete)
> +		__fsnotify_inode_delete(inode);
>  }
>  
>  /*
> -- 
> 1.9.3
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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