linux-kernel - Re: [PATCH v5 bpf-next 0/5] bpf path iterator

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Message-ID: <CAPhsuW7EyTTh-qkrA86ERfSUUJK0o1Jz1UKH+o6rMY1-QioJRA@mail.gmail.com>
Date: Wed, 2 Jul 2025 22:04:46 -0700
From: Song Liu <song@...nel.org>
To: Mickaël Salaün <mic@...ikod.net>, brauner@...nel.org
Cc: bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org, 
	kernel-team@...a.com, andrii@...nel.org, eddyz87@...il.com, ast@...nel.org, 
	daniel@...earbox.net, martin.lau@...ux.dev, viro@...iv.linux.org.uk, 
	jack@...e.cz, kpsingh@...nel.org, mattbobrowski@...gle.com, m@...wtm.org, 
	neil@...wn.name, Günther Noack <gnoack@...gle.com>
Subject: Re: [PATCH v5 bpf-next 0/5] bpf path iterator

Hi Christian,

On Tue, Jun 24, 2025 at 11:46 AM Mickaël Salaün <mic@...ikod.net> wrote:
>
> On Fri, Jun 20, 2025 at 02:59:17PM -0700, Song Liu wrote:
> > Hi Christian, Mickaël, and folks,
> >
> > Could you please share your comments on this version? Does this
> > look sane?
>
> This looks good to me but we need to know what is the acceptable next
> step to support RCU.  If we can go with another _rcu helper, I'm good
> with the current approach, otherwise we need to figure out a way to
> leverage the current helper to make it compatible with callers being in
> a RCU read-side critical section while leveraging safe path walk (i.e.
> several calls to path_walk_parent).

Could you please share your suggestions on this topic? RCU
protected path walk out of fs/ seems controversial in multiple
ways. Do we have to let this set wait indefinitely for a solution
of RCU protected path walk? I would like to highlight that this
set doesn't add any persistent APIs. path_walk_parent() is not
in the UAPI, nor exported. If a newer and better API is created,
we can refactor bpf and landlock code and deprecate
path_walk_parent().

Thanks,
Song