linux-kernel - Re: [RFC PATCH 04/10] liveupdate: flb: allow getting FLB data in early boot

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Message-ID: <CA+CK2bDWF6pbNQRkJFa+WcD1pwUOr3yQdrRUs-mgLWu5ght+7A@mail.gmail.com>
Date: Sat, 20 Dec 2025 10:11:34 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Mike Rapoport <rppt@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Muchun Song <muchun.song@...ux.dev>, 
	Oscar Salvador <osalvador@...e.de>, Alexander Graf <graf@...zon.com>, David Matlack <dmatlack@...gle.com>, 
	David Rientjes <rientjes@...gle.com>, Jason Gunthorpe <jgg@...dia.com>, 
	Samiullah Khawaja <skhawaja@...gle.com>, Vipin Sharma <vipinsh@...gle.com>, 
	Zhu Yanjun <yanjun.zhu@...ux.dev>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	linux-doc@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [RFC PATCH 04/10] liveupdate: flb: allow getting FLB data in
 early boot

> > [Follow-up from LPC discussion]
> >
> > This patch is not needed, you can use liveupdate_flb_get_incoming()
> > directly in early boot. The main concern is that we take mutex in that
> > function, but that I think is safe. The might_sleep() has the proper
> > handling to be called early in boot, it has "system_state ==
> > SYSTEM_BOOTING" check to silence warning during boot.
>
> Right. I will give it a try. For hugetlb, this works fine since it
> doesn't really need to do much in FLB retrieve anyway, it just needs to
> parse some data structures.
>
> If other subsystems end up needing a two-part retrieve, one in early
> boot and one later, then I think it would be a good idea to model that
> properly instead of leaving it up to the subsystem to manage it.
>
> Anyway, that isn't a real problem today so let's look at it when it does
> show up.

FLB has exactly one .retrieve() lifecycle event. Once called, the data
is considered fully available and cached in private->incoming.obj.

If a subsystem has a requirement where it needs a specific state
available very early and other state available much later, the clean
solution is simply to register two separate FLBs.

Pasha