linux-kernel - Re: [RESEND PATCH v2] modules: wait do_free

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Date: Mon, 29 Jan 2024 09:53:58 -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,
	Xiaoyi Su <suxiaoyi@...wei.com>
Subject: Re: [RESEND PATCH v2] modules: wait do_free_init correctly

On Mon, Jan 29, 2024 at 10:03:04AM +0800, Changbin Du wrote:
> The commit 1a7b7d922081 ("modules: Use vmalloc special flag") moves
> do_free_init() into a global workqueue instead of call_rcu(). So now
> rcu_barrier() can not ensure that do_free_init has completed. We should
> wait it via flush_work().
> 
> Without this fix, we still could encounter false positive reports in
> W+X checking, and rcu synchronization is unnecessary.

You didn't answer my question, which should be documented in the commit log.

Does this mean we never freed modules init because of this? If so then
your commit log should clearly explain that. It should also explain that
if true (you have to verify) then it means we were no longer saving
the memory we wished to save, and that is important for distributions
which do want to save anything on memory. You may want to do a general
estimate on how much that means these days on any desktop / server.

  Luis