linux-kernel - Re: [PATCH 1/1] sched.h: always_inline alloc_tag

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Message-ID: <CAJuCfpFGRmQXxkaUjasyVGu74su_a-319o5zYe_eJD_KfbmNdg@mail.gmail.com>
Date: Wed, 3 Jul 2024 16:23:27 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, 
	vincent.guittot@...aro.org, kent.overstreet@...ux.dev, 
	linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/1] sched.h: always_inline alloc_tag_{save|restore} to
 fix modpost warnings

On Wed, Jul 3, 2024 at 3:51 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Wed,  3 Jul 2024 15:15:20 -0700 Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> > Mark alloc_tag_{save|restore} as always_inline to fix the following
> > modpost warnings:
> >
> > WARNING: modpost: vmlinux: section mismatch in reference: alloc_tag_save+0x1c (section: .text.unlikely) -> initcall_level_names (section: .init.data)
> > WARNING: modpost: vmlinux: section mismatch in reference: alloc_tag_restore+0x3c (section: .text.unlikely) -> initcall_level_names (section: .init.data)
>
> Well, is it only about fixing warnings?  If the warning is correct then
> this might be fixing kernel crashes.
>
> Do you know where these references are coming from?

I *think* this happens when alloc_tag_save()/alloc_tag_restore() are
not inlined and are called from an __init function.  They access the
`tag` parameter passed to them and since that tag is a static local
variable inside an __init function, I assume it gets allocated inside
__initdata. If so, an example of such case is cma_activate_area()
which is an __init function and allocates memory using
bitmap_zalloc():
https://elixir.bootlin.com/linux/v6.10-rc6/source/mm/cma.c#L97. There
are likely more cases like that.

>
> I'm curious about the .text.unlikely.  Makes me wonder if we should
> also have .init.unlikely for unlikely() calls which happen from __init
> code.  Maybe we already handle that.

I don't really know.

>
> > Reported-by: kernel test robot <lkp@...el.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202407032306.gi9nZsBi-lkp@intel.com/
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > Cc: Kent Overstreet <kent.overstreet@...ux.dev>
>
> Fixes: 22d407b164ff ("lib: add allocation tagging support for memory allocation profiling")

Yes. Do you want me to post a v2 or will handle that locally?

> Cc: stable

I don't think so. This feature was introduced in 6.10, so no backports
needed, right?

>
> yes?
>
>