linux-kernel - Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount

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Message-ID: <52210A55.8010308@hp.com>
Date:	Fri, 30 Aug 2013 17:10:45 -0400
From:	Waiman Long <waiman.long@...com>
To:	Al Viro <viro@...IV.linux.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeff Layton <jlayton@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless
 update of refcount

On 08/30/2013 04:54 PM, Al Viro wrote:
> On Fri, Aug 30, 2013 at 01:43:11PM -0700, Linus Torvalds wrote:
>> On Fri, Aug 30, 2013 at 1:15 PM, Waiman Long<waiman.long@...com>  wrote:
>>> The prepend_path() isn't all due to getcwd. The correct profile should be
>> Ugh. I really think that prepend_path() should just be rewritten to
>> run entirely under RCU.
>>
>> Then we can remove *all* the stupid locking, and replace it with doing
>> a read-lock on the rename sequence count, and repeating if requited.
>>
>> That shouldn't even be hard to do, it just requires mindless massaging
>> and being careful.
> Not really.  Sure, you'll retry it if you race with d_move(); that's not
> the real problem - access past the end of the object containing ->d_name.name
> would screw you and that's what ->d_lock is preventing there.  Delayed freeing
> of what ->d_name is pointing into is fine, but it's not the only way to get
> hurt there...

Actually, prepend_path() was called with rename_lock taken. So d_move() 
couldn't be run at the same time. Am I right?

Regards,
Longman
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