linux-kernel - Re: [PATCH v2 1/2] init/initramfs.c: allow asynchronous unpacking

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Message-ID: <9cf7863f-742b-1cfd-1027-04e314467e01@prevas.dk>
Date:   Tue, 9 Mar 2021 23:39:47 +0100
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 1/2] init/initramfs.c: allow asynchronous unpacking

On 09/03/2021 23.07, Linus Torvalds wrote:
> On Tue, Mar 9, 2021 at 1:17 PM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
>>
>> So add an initramfs_async= kernel parameter, allowing the main init
>> process to proceed to handling device_initcall()s without waiting for
>> populate_rootfs() to finish.
> 
> I like this smaller second version of the patch, but am wondering why
> we even need the parameter.
> 
> It sounds mostly like a "maybe I didn't think of all cases" thing -

That's exactly what it is.

> and one that will mean that this code will not see a lot of actual
> test coverage..

Yeah, that's probably true.

> And because of the lack of test coverage, I'd rather reverse the
> meaning, and have the async case on by default (without even the
> Kconfig option), and have the kernel command line purely as a "oops,
> it's buggy, easy to ask people to test if this is what ails them".

Well, I wasn't bold enough to make it "default y" by myself, but I can
certainly do that and nuke the config option.

> What *can* happen early boot outside of firmware loading and usermodehelpers?

Well, that was what I tried to get people to tell me when I sent the
first version as RFC, and also before that
(https://lore.kernel.org/lkml/19574912-44b4-c1dc-44c3-67309968d465@rasmusvillemoes.dk/).
That you can't think of anything suggests that I have covered the
important cases - which does leave random drivers that poke around the
filesystem on their own, but (a) it would probably be a good thing to
have this flush those out and (b) there's the command line option to
make it boot anyway.

Rasmus