linux-kernel - Re: [PATCH] modules: wait do_free

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Message-ID: <ZYL7B59dQ6XFtVP8@bombadil.infradead.org>
Date: Wed, 20 Dec 2023 06:32:39 -0800
From: Luis Chamberlain <mcgrof@...nel.org>
To: Changbin Du <changbin.du@...wei.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
	Hui Wang <hw.huiwang@...wei.com>, Xiaoyi Su <suxiaoyi@...wei.com>,
	Jeffrey Hugo <jhugo@...eaurora.org>
Subject: Re: [PATCH] modules: wait do_free_init correctly

On Wed, Dec 20, 2023 at 01:27:51PM +0800, Changbin Du wrote:
> On Tue, Dec 19, 2023 at 01:52:03PM -0800, Luis Chamberlain wrote:
> > On Tue, Dec 19, 2023 at 12:51:51PM -0800, Andrew Morton wrote:
> > > On Tue, 19 Dec 2023 22:12:31 +0800 Changbin Du <changbin.du@...wei.com> wrote:
> > > 
> > > > The commit 1a7b7d922081 ("modules: Use vmalloc special flag") moves
> > > > do_free_init() into a global workqueue instead of call_rcu(). So now
> > > > we should wait it via flush_work().
> > > 
> > > What are the runtime effects of this change?
> > 
> > Indeed that's needed given how old this culprit commit is:
> > 
> > git describe --contains 1a7b7d922081
> > v5.2-rc1~192^2~5
> > 
> > Who did this work and for what reason? What triggered this itch?
> >
> Seems the waiting was introduced by commit ae646f0b9ca ("init: fix false positives
> in W+X checking").
> 
> As what I have observed, mark_readonly() is only invoked by the first user mode
> thread function kernel_init(), which is before userspace /init. So is it real
> possible we have loaded modules at this point?

Are you saying we don't free any module inits at all then? I asked a lot
of questions and your answers seem slim.

How did you find this?
What actual impact does this have without the patch?

The commit must document this.

  Luis