netdev - Re: [PATCH v3 24/25] sunrpc: Change how dentry's d

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Message-ID: <20130704042034.GM4165@ZenIV.linux.org.uk>
Date:	Thu, 4 Jul 2013 05:20:34 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Waiman Long <Waiman.Long@...com>
Cc:	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v3 24/25] sunrpc: Change how dentry's d_lock field is
 accessed

On Wed, Jul 03, 2013 at 04:25:32PM -0400, Waiman Long wrote:
> There is no change in logic and everything should just work.

> -		spin_lock(&file->f_path.dentry->d_lock);
> +		d_lock(file->f_path.dentry);
>  		if (!d_unhashed(file->f_path.dentry))
>  			clnt = RPC_I(inode)->private;
>  		if (clnt != NULL && atomic_inc_not_zero(&clnt->cl_count)) {
> -			spin_unlock(&file->f_path.dentry->d_lock);
> +			d_unlock(file->f_path.dentry);

Could somebody explain WTF is being protected here?  It's not ->private -
that gets set (and, more importantly, cleared) without ->d_lock in sight.
Trond, that seems to be your code from about three years ago (introduced
in "SUNRPC: Fix a race in rpc_info_open").  What's going on there?
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