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

From: Luis Chamberlain <mcgrof@kernel.org>
To: Bruno Goncalves <bgoncalv@redhat.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Alexander Egorenkov <egorenar@linux.ibm.com>,
	akpm@linux-foundation.org, bp@alien8.de, corbet@lwn.net,
	gregkh@linuxfoundation.org, jeyu@kernel.org,
	linux-kernel@vger.kernel.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	torvalds@linux-foundation.org, Dave Young <dyoung@redhat.com>
Subject: Re: [PATCH v3 1/2] init/initramfs.c: do unpacking asynchronously
Date: Tue, 27 Jul 2021 07:42:46 -0700	[thread overview]
Message-ID: <YQAbZhCwLS7vb/ag@bombadil.infradead.org> (raw)
In-Reply-To: <CA+QYu4ofYOqcuCYohFnYYO+XhAjKfpyGQ4KJr5vE4Fo=whv7UA@mail.gmail.com>

On Tue, Jul 27, 2021 at 04:27:08PM +0200, Bruno Goncalves wrote:
> On Tue, Jul 27, 2021 at 4:21 PM Luis Chamberlain <mcgrof@kernel.org> wrote:
> >
> > On Tue, Jul 27, 2021 at 04:12:54PM +0200, Bruno Goncalves wrote:
> > > On Tue, Jul 27, 2021 at 3:55 PM Luis Chamberlain <mcgrof@kernel.org> wrote:
> > > >
> > > > 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@rasmusvillemoes.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?
> > >
> > > No, the machines we were able to reproduce the problem don't have drdb.
> >
> > Are there *any* umh calls early on boot on the s390 systems? If so
> > chances are that is the droid you are looking for.
> 
> Sorry Luis,
> 
> I was just replying the question mentioning an old thread
> (https://lore.kernel.org/lkml/CA+QYu4qxf2CYe2gC6EYnOHXPKS-+cEXL=MnUvqRFaN7W1i6ahQ@mail.gmail.com/T/#u)
> on ppc64le.
> 
> regarding the "umh" it doesn't show anything on ppc64le boot.

There is not a single pr_*() call on kernel/umh.c, and so unless the
respective ppc64le / s390 umh callers have a print, we won't know if you
really did use a print.

Can you reproduce the failure? How often?

  Luis