Re: [PATCH v7 1/4] spinlock: A new lockref structure for locklessupdate of refcount

[Al Viro]

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@xxxxxx> 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...
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