linux-kernel - Re: [PATCH v2] alloc_tag: fix rw permission issue when handling boot parameter

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Message-ID: <CAJuCfpEFZNwmpwfUqM45StJKPZG3s+qZpv8Vy2ohF6StsL4LGg@mail.gmail.com>
Date: Wed, 14 Jan 2026 20:58:52 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: ranxiaokai627@....com, kent.overstreet@...ux.dev, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, ran.xiaokai@....com.cn
Subject: Re: [PATCH v2] alloc_tag: fix rw permission issue when handling boot parameter

On Wed, Jan 14, 2026 at 7:23 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Thu, 15 Jan 2026 03:15:36 +0000 ranxiaokai627@....com wrote:
>
> > From: Ran Xiaokai <ran.xiaokai@....com.cn>
> >
> > Boot parameters prefixed with "sysctl." are processed
> > during the final stage of system initialization via kernel_init()->
> > do_sysctl_args(). When CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled,
> > the sysctl.vm.mem_profiling entry is not writable and will cause
> > a warning.
>
> This sounds strange.  Why would setting a Kconfig debug thing disable
> alteration of a runtime control?

If debug is enabled we don't want the users toggling profiling on and
off because all allocations made while profiling is off will have no
tags. If used later enables profiling and these allocations get freed,
each one will prodice a warning about missing tag. We want to avoid
that by disallowing to toggle this control at runtime when debugging
is enabled.

> Documentation/mm/allocation-profiling.rst provided no hint.

True. I'll post a patch to add that limitation there with description why.

>
> > Before run_init_process(), system initialization executes in kernel
> > thread context. Use current->mm to distinguish sysctl writes during
> > do_sysctl_args() from user-space triggered ones.
> >
> > And when the proc_handler is from do_sysctl_args(), always return success
> > because the same value was already set by setup_early_mem_profiling()
> > and this eliminates a permission denied warning.
> >
> > Suggested-by: Suren Baghdasaryan <surenb@...gle.com>
> > Acked-by: Suren Baghdasaryan <surenb@...gle.com>
> > Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
>
> Should we backport it?

I'm not sure a single boot time warning produced only in debug mode
warrants backporting. Do you think we should do it anyway?