[PATCH review 0/7] Bind mount escape fixes

Linus Torvalds torvalds at linux-foundation.org
Sun Aug 16 02:25:41 UTC 2015


On Sat, Aug 15, 2015 at 7:12 PM, Al Viro <viro at zeniv.linux.org.uk> wrote:
>
> I think you are underestimating the frequency of .. traversals.  Any build
> process that creates relative symlinks will be hitting it all the time,
> for one thing.

I suspect you're over-estimating how expensive it is to just walk down
to the mount-point. It's just a few pointer traversals.

Realistically, we probably do more than that for a *regular* path
component lookup, when we follow the hash chains. Following a d_parent
chain for ".." isn't that different.

Just looking at the last patch Eric sent, that one looks _trivial_. It
didn't need *any* preparation or new rules. Compared to the mess with
marking things MNT_DIR_ESCAPED etc, I know which approach I'd prefer.

But hey, if you think you can simplify it... I just don't think that
even totally ignoring the d_splice_alias() things, and totally
ignoring any locking around __d_move(), the whole "mark things
MNT_DIR_ESCAPED" is a lot more complex.

              Linus


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