+ init-mount-print-pretty-name-of-root-device-when-panics.patch added to mm-nonmm-unstable branch

+ init-mount-print-pretty-name-of-root-device-when-panics.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: init/mount: print pretty name of root device when panicing
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     init-mount-print-pretty-name-of-root-device-when-panics.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/init-mount-print-pretty-name-of-root-device-when-panics.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jianyong Wu <jianyong.wu@arm.com>
Subject: init/mount: print pretty name of root device when panicing
Date: Thu, 7 Sep 2023 09:10:25 +0000

Given a wrong root device, current log may not give the pretty name
which is useful to locate root cause.

For example, there are 2 blk devs in a VM, /dev/vda which has 2 partitials
/dev/vda1 and /dev/vda2 and /dev/vdb which is blank.  /dev/vda2 is the
right root dev.  When set "root=/dev/vdb", we get error log:

[    0.635575] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(254,16)

It's not straightforward to find out the root cause as there is lack of
the root devive name therefore hard for people to get those info from the
device number, in the example, (254,16).

It is more comprehensive way to hint the root cause if pretty name is
given here, like:

[    0.559887] Kernel panic - not syncing: VFS: Unable to mount root fs on "/dev/vdb" or unknown-block(254,16)

Link: https://lkml.kernel.org/r/20230907091025.3436878-1-jianyong.wu@arm.com
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Justin He <justin.he@arm.com>
Cc: Loic Poulain <loic.poulain@linaro.org>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 init/do_mounts.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/init/do_mounts.c~init-mount-print-pretty-name-of-root-device-when-panics
+++ a/init/do_mounts.c
@@ -244,7 +244,7 @@ retry:
 	for (i = 0, p = fs_names; i < num_fs; i++, p += strlen(p)+1)
 		printk(" %s", p);
 	printk("\n");
-	panic("VFS: Unable to mount root fs on %s", b);
+	panic("VFS: Unable to mount root fs on \"%s\" or %s", pretty_name, b);
 out:
 	put_page(page);
 }
_

Patches currently in -mm which might be from jianyong.wu@arm.com are

init-mount-print-pretty-name-of-root-device-when-panics.patch