Re: [PATCH] namei: clear nd->root.mnt before O_CREAT unlazy

[Brian Foster <bfoster@redhat.com>]

On Fri, Jan 07, 2022 at 07:10:59AM +0000, Al Viro wrote:
> On Fri, Jan 07, 2022 at 05:52:27AM +0000, Al Viro wrote:
> 
> > > Looks good, assuming Al is ok with the re-factoring.
> > > Reviewed-by: Ian Kent <raven@themaw.net>
> > 
> > Ummm....  Mind resending that?  I'm still digging myself from under
> > the huge pile of mail, and this seems to have been lost in process...
> 
> Non-obvious part is that current code only does this forgetting
> the root when we are certain that we won't look at it later in
> pathwalk.  IOW, it's guaranteed to be the same through the entire
> thing.  This patch changes that; the final component may very well
> be e.g. an absolute symlink.  We won't know that until we unlazy,
> so we can't make forgetting conditional upon that.
> 
> I _think_ it's not going to lead to any problems, but I'll need to
> take a good look at the entire thing after I get some sleep -
> I'm about to fall down right now.
> 

Heh, Ok. I think I understand what you're getting at, but I'd have to
stare at the code much more to grok the details. Let me know if you
think the logic and/or commit log needs to change wrt to this and I'll
give it a shot.

> Other problems here (aside of whitespace damage - was that a
> cut'n'paste of some kind?  Looks like 8859-1 NBSP for each
> leading space...) are

Hmm.. I don't see any whitespace damage, even if I pull the patch back
from the mailing list into my tree..?

> 	* misleading name of the new helper - it sounds like
> "non-RCU side of complete_walk()" and that's not what it does

The intent was the opposite, of course. :P I'm not sure how you infer
the above from _rcu(), but I'll name the helper whatever. Suggestions?

> 	* LOOKUP_CACHED needs to be mentioned in commit message
> (it's incompatible with O_CREAT, so it couldn't occur on that
> codepath - the transformation is an equivalent one, but that
> ought to be mentioned)

Ok. I can add a "for non-create path only" comment to that effect in the
helper as well if useful.

> 	* the change I mentioned above needs to be in commit
> message - this one is a lot more subtle.
> 

Ack.

> Anyway, I'll look into that tomorrow - too sleepy right now
> to do any serious analysis.
> 

Ack. Thanks for the first pass.

Brian