linux-kernel - Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS

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Date:   Sat, 16 Sep 2017 23:03:19 -0500
From:   Rob Landley <rob@...dley.net>
To:     Christophe LEROY <christophe.leroy@....fr>,
        Michael Ellerman <mpe@...erman.id.au>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     sachinp <sachinp@...ux.vnet.ibm.com>, mhocko@...e.com,
        peterz@...radead.org, viresh.kumar@...aro.org,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        mingo@...nel.org, lokeshvutla@...com,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        linux-input@...r.kernel.org, thomas.lendacky@....com,
        lauraa@...eaurora.org, keescook@...omium.org,
        Jiri Kosina <jikos@...nel.org>, rostedt@...dmis.org,
        linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
        tglx@...utronix.de, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, tj@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

On 09/14/2017 04:17 AM, Christophe LEROY wrote:
> Le 14/09/2017 à 01:51, Rob Landley a écrit :
>> From: Rob Landley <rob@...dley.net>
>>
>> Make initramfs honor CONFIG_DEVTMPFS_MOUNT, and move
>> /dev/console open after devtmpfs mount.
>>
>> Add workaround for Debian bug that was copied by Ubuntu.
> 
> Is that a bug only for Debian ? Why ?

Look down, specifically this bit:

>> v2 discussion:
>> http://lkml.iu.edu/hypermail/linux/kernel/1705.2/05611.html

That's some discussion of version 2 of this patch, which was merged for
a while last dev cycle, then backed out again because it triggered the
same bug in a number of system init scripts:

  http://lkml.iu.edu/hypermail/linux/kernel/1705.2/07072.html
  http://lkml.iu.edu/hypermail/linux/kernel/1705.3/01182.html
  http://lkml.iu.edu/hypermail/linux/kernel/1705.3/01505.html
  http://lkml.iu.edu/hypermail/linux/kernel/1705.3/01320.html

All of whom copied the broken error "recovery" path from debian. If they
checked whether it was already mounted, or didn't _blank_ the /dev
directory in response to mounting the exact same filesystem over itself
giving -EBUSY, the system would work fine. Heck, if you built a kernel
with a static /dev in initramfs and no devtmpfs configured in, the
script would break things exactly the same way. The breakage is that
script takes a hammer to a perfectly functional /dev directory and then
continues the boot with an empty /dev. That's bonkers.

> Why should a Debian bug be fixed by a workaround in the mainline kernel ?

That was my argument last time, and the answer was "Breaking userspace
is bad, mmmkay." Even when userspace is doing something REALLY OBVIOUSLY
STUPID and it is _clearly_ their fault, as long as they got there first
they've established the status quo and it doesn't matter how silly it is.

This was explicitly stated to me here:

  http://lkml.iu.edu/hypermail/linux/kernel/1705.3/03292.html

I.E. don't argue with me, argue with him. :)

So, I added a workaround with a printk in hopes of embarassing them into
someday fixing it.

Rob