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

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

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.

> 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.


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