linux-kernel - Re: [PATCH v3 1/2] init/initramfs.c: do unpacking asynchronously

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Message-ID: <YQAQFMDMk09wS6Qv@bombadil.infradead.org>
Date:   Tue, 27 Jul 2021 06:54:28 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Bruno Goncalves <bgoncalv@...hat.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>,
        akpm@...ux-foundation.org, bp@...en8.de, corbet@....net,
        gregkh@...uxfoundation.org, jeyu@...nel.org,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        torvalds@...ux-foundation.org, Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v3 1/2] init/initramfs.c: do unpacking asynchronously

On Tue, Jul 27, 2021 at 09:31:54AM +0200, Bruno Goncalves wrote:
> On Mon, Jul 26, 2021 at 1:46 PM Rasmus Villemoes
> <linux@...musvillemoes.dk> wrote:
> >
> > On 24/07/2021 09.46, Alexander Egorenkov wrote:
> > > Hello,
> > >
> > > since e7cb072eb988 ("init/initramfs.c: do unpacking asynchronously"), we
> > > started seeing the following problem on s390 arch regularly:
> > >
> > > [    5.039734] wait_for_initramfs() called before rootfs_initcalls

So some context here, which might help.

The initramfs_cookie is initialized until a a rootfs_initcall() is
called, in this case populate_rootfs(). The code is small, so might
as well include it:

static int __init populate_rootfs(void)
{
	initramfs_cookie = async_schedule_domain(do_populate_rootfs, NULL,
						 &initramfs_domain);
	if (!initramfs_async)
		wait_for_initramfs();
	return 0;
}                                                                               
rootfs_initcall(populate_rootfs);

The warning you see comes from a situation where a wait_for_initramfs()
gets called but we haven't yet initialized initramfs_cookie.  There are
only a few calls for wait_for_initramfs() in the kernel, and the only
thing I can think of is that somehow s390 may rely on a usermode helper
early on, but not every time.

What umh calls does s390 issue?

> Unfortunately, we haven't been able to find the root cause, but since
> June 23rd we haven't hit this panic...
> 
> Btw, this panic we were hitting only when testing kernels from "scsi"
> and "block" trees.

Do you use drdb maybe?

  Luis