linux-kernel - Re: [git pull] vfs pile 1

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Message-ID: <20120109151129.GA22175@thunk.org>
Date:	Mon, 9 Jan 2012 10:11:29 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
Subject: Re: [git pull] vfs pile 1

On Sun, Jan 08, 2012 at 11:50:40PM +0000, Al Viro wrote:
> 
> WTF is ext4_symlink() doing in case of long symlinks?  Look:
>                 drop_nlink(inode);
>                 err = ext4_orphan_add(handle, inode);
>                 ext4_journal_stop(handle);
> [write symlink body]
>                 inc_nlink(inode);
>                 err = ext4_orphan_del(handle, inode);
> oh, I see...  The comment above that re deadlocks and inability to do that
> in a single transaction ;-/
> 
> OK, try this; that's equivalent to what they are doing and will not WARN_ON();
> I hadn't checked other filesystems for similar tricks yet, so this has a good
> chance of being incomplete.
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 86edc45..2043f48 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -2315,7 +2315,7 @@ retry:
>  			err = PTR_ERR(handle);
>  			goto err_drop_inode;
>  		}
> -		inc_nlink(inode);
> +		set_nlink(inode, 1);
>  		err = ext4_orphan_del(handle, inode);
>  		if (err) {
>  			ext4_journal_stop(handle);

Thanks, looks good to me.

Acked-by: "Theodore Ts'o" <tytso@....edu>

What's there is a bit of kludge, granted.  But an attempt to optimize
out placing the inode on and off the orphan list (either by deferring
the start of the ext3/4 journal handle, or by special casing the block
used for the long symlink) would add a lot of complexity, and creating
long symlinks is not common case in most workloads...

						- Ted
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