Re: [PATCH v2] vfs: Don't exchange "short" filenames unconditionally.

[Linus Torvalds]

On Mon, Sep 29, 2014 at 8:59 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> Now RCU lookup starts.  And on another CPU we move the first dentry over
> the third one.  copy_name() is called, it decrements the refcount down
> to 1 (__d_free() hasn't happened yet) and doesn't schedule any freeing.

Ahh. If we were to do *all* of the copy-name name freeing under RCU,
we'd be ok. But we don't. We do the refcount decrement immediately
(and have to, if we want to have the rcu/refcount union). Yeah, good
call, although I find that doubvle rcu grace period for the common
case to be very annoying.

Ugh. I'm starting to be sorry I ever suggested this cleanup. Maybe
we're better off with the horrid hack (which is equivalent to what we
did before) after all.

               Linus
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