Re: [Dev] Hikey mounting rootfs failure on linux-next branch

On 24/05/17 05:34, Leo Yan wrote:

Hi,

When verified some patches on linux-next branch I found Debian rootfs cannot be mounted successfully on Hikey, the booting log is: http://termbin.com/akar

From the log, we can see: mount: mounting udev on /dev failed: Device or resource busy ... ALERT! /dev/disk/by-partlabel/system does not exist. Dropping to a shell!

So I bisected the linux-next branch and narrow down below patch which introduces mounting failure; after applied this patch, the kernel will mount devtmpfs on '/dev', then later udev cannot mount again for devfs. Finally cannot find '/dev/disk/by-partlabel/system' for rootfs.

I don't know what's the best way to fix this issue, welcome any suggestion for this. And report this issue in case it may impact later Debian release?

I'd get this out onto LKML. Finding bugs in patches is what linux-next is for (though do check that there are not already active thread on this).

It might be good to know whether it is the movement of the /dev/console code or the extra branch that causes the problem. I assume that the problem happens because /dev/console is opened from devtmpfs but I'm not entirely sure.

Daniel.

Thanks, Leo Yan

---8<---

From ee35011fd0324b37fbb046561e58d4d6bae798ac Mon Sep 17 00:00:00 2001 From: Rob Landley rob@landley.net Date: Fri, 19 May 2017 07:39:23 +1000 Subject: [PATCH] initramfs: make initramfs honor CONFIG_DEVTMPFS_MOUNT

Make initramfs honor CONFIG_DEVTMPFS_MOUNT, fixing 2b2af54a5bb6 ("Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev"), which didn't bother. Move /dev/console open after devtmpfs mount, and update help text.

Commit 456eeabab849 in 2005 made gen_initramfs_list (when run with no arguments) spit out an 'example' config creating /dev and /dev/console. The kernel accidentally(?) included this for many years when you didn't specify initramfs contents, and of course grew dependencies on this /dev/console node in the (often hidden) initramfs. c33df4eaaf41 ("disable init/initramfs.c") in 2007 explicitly preserved this dependency. 2bd3a997befc ("init: Open /dev/console from rootfs") in 2010 claimed it "removes the occasionally problematic assumption that /dev/console exists from the boot code" but actually just moved it later.

But nobody never tested statically linking an initramfs. If you point CONFIG_INITRAMFS_SOURCE at a directory running the build as a normal user you _don't_ get a /dev/console (because you can't create it without being root, and can't use the existing one out of /dev unless you create your own initramfs list file), in which case init runs with stdin/stdout/stderr closed and you get no output.

Eric's test case for his 2010 commit referenced above was:

With this patch I was able to throw busybox on my /boot partition (which has no /dev directory) and boot into userspace without problems.

But it didn't work pointing CONFIG_INITRAMFS_SOURCE at a directory of the same files. This provides the "automatically mounting devtmpfs on /dev" workaround the earlier commit was trying to avoid.

Link: http://lkml.kernel.org/r/21935caf-501d-e97c-5611-5c4af7e0f9ae@landley.net Signed-off-by: Rob Landley rob@landley.net Cc: Eric W. Biederman ebiederm@xmission.com Cc: Jean-Paul Saman jean-paul.saman@nxp.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Prarit Bhargava prarit@redhat.com Cc: Yang Shi yang.shi@linaro.org Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Cc: Kees Cook keescook@chromium.org Cc: Emese Revfy re.emese@gmail.com Cc: Petr Mladek pmladek@suse.com Cc: Fabian Frederick fabf@skynet.be Signed-off-by: Andrew Morton akpm@linux-foundation.org

---

drivers/base/Kconfig | 14 ++++---------- init/main.c | 15 +++++++++------ 2 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index d718ae4..74779ee 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -48,16 +48,10 @@ config DEVTMPFS_MOUNT bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs" depends on DEVTMPFS help

•  This will instruct the kernel to automatically mount the
  

•  devtmpfs filesystem at /dev, directly after the kernel has
  

•  mounted the root filesystem. The behavior can be overridden
  

•  with the commandline parameter: devtmpfs.mount=0|1.
  

•  This option does not affect initramfs based booting, here
  

•  the devtmpfs filesystem always needs to be mounted manually
  

•  after the rootfs is mounted.
  

•  With this option enabled, it allows to bring up a system in
  

•  rescue mode with init=/bin/sh, even when the /dev directory
  

•  on the rootfs is completely empty.
  

•  Automatically mount devtmpfs at /dev on the root filesystem, which
  

•  lets the system to come up in rescue mode with [rd]init=/bin/sh.
  

•  Override with devtmpfs.mount=0 on the commandline. Initramfs can
  

•  create a /dev dir as needed, other rootfs needs the mount point.
  

config STANDALONE bool "Select only drivers that don't need compile-time external firmware" diff --git a/init/main.c b/init/main.c index f866510..9ec09ff 100644 --- a/init/main.c +++ b/init/main.c @@ -1038,12 +1038,6 @@ static noinline void __init kernel_init_freeable(void) do_basic_setup();

• /* Open the /dev/console on the rootfs, this should never fail */
• if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)

• pr_err("Warning: unable to open an initial console.\n");
  

• (void) sys_dup(0);
• (void) sys_dup(0); /*
  • check if there is an early userspace init. If yes, let it do all
  • the work

@@ -1055,8 +1049,17 @@ static noinline void __init kernel_init_freeable(void) if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) { ramdisk_execute_command = NULL; prepare_namespace();

• } else if (IS_ENABLED(CONFIG_DEVTMPFS_MOUNT)) {

• sys_mkdir("/dev", 0755);
  

• devtmpfs_mount("/dev");
  

  }

• /* Open the /dev/console on the rootfs, this should never fail */
• if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)

• pr_err("Warning: unable to open an initial console.\n");
  

• (void) sys_dup(0);
• (void) sys_dup(0);
• /*
  • Ok, we have completed the initial bootup, and
  • we're essentially up and running. Get rid of the