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

[Bruno Goncalves]

On Mon, Jul 26, 2021 at 1:46 PM Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> 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
>
> While that message was added as part of the same patch, it's a red
> herring: It merely means that something ends up calling usermodehelper
> (perhaps a request_module) before the init sequence has come around to
> rootfs_initcalls. At that point, the rootfs is (with or without my async
> patch) entirely empty, so those usermodehelper calls have always failed
> with -ENOENT.
>
> If you have CONFIG_UEVENT_HELPER=y and CONFIG_UEVENT_HELPER_PATH set to
> a non-empty string, you can try setting the latter to the empty string.
> But the message won't go away if it's really a request_module() and not
> a uevent notification.
>
> > [    6.599433] rootfs image is not initramfs (broken padding); looks like an initrd
> > [    6.669373] Freeing initrd memory: 24828K
> >
> > It is very hard to reproduce, i haven't managed to do it yet and working
> > on it, but it occurs regularly, nearly every day once but only on a particular
> > test machine with our nightly s390 CI test runs.
>
> So this looks somewhat similar to a ppc64 report
>
> https://lore.kernel.org/lkml/CA+QYu4qxf2CYe2gC6EYnOHXPKS-+cEXL=MnUvqRFaN7W1i6ahQ@xxxxxxxxxxxxxx/T/#u
>
> that ended up not being caused by e7cb072eb988, since it could also be
> reproduced with that patch reverted. I don't know if Bruno found the
> root cause, adding him to cc. Also cc += Dave Young who had some input
> in that thread.

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.

Bruno
>
> > Although the initramfs corruption is hard to reproduce,
> > the message 'wait_for_initramfs() called before rootfs_initcalls'
> > appears regularly on each boot at least since 2021-06-24 which we just
> > noticed a couple of days ago.
> >
> > Appending 'initramfs_async=0' to the kernel command-line doesn't seem to
> > help with the 'wait_for_initramfs' message and i can still see it.
>
> Yes, that's expected. I should probably send a patch to move
> usermodehelper_enable() from do_basic_setup() to populate_rootfs(), as
> it really doesn't make sense to have usermodehelper enabled before
> there's any content in the file system. But as I said, the warning is
> harmless and merely indicates there's a bunch of futile work being done
> to call a (at that point in time) non-existing usermode program.
>
> > [    0.890962] wait_for_initramfs() called before rootfs_initcalls
> ...
> > [    1.636419] Trying to unpack rootfs image as initramfs...
> > [    1.676907] Freeing initrd memory: 26056K
>
> It would be interesting if you could boot with initramfs_async=0 enough
> times to see if you can reproduce the problem; and/or do the same with
> e7cb072eb988 reverted.
>
> Thanks,
> Rasmus
>