From: Rob Landley <[email protected]>
Make initramfs honor CONFIG_DEVTMPFS_MOUNT, and move
/dev/console open after devtmpfs mount.
Add workaround for Debian bug that was copied by Ubuntu.
Signed-off-by: Rob Landley <[email protected]>
---
v2 discussion: http://lkml.iu.edu/hypermail/linux/kernel/1705.2/05611.html
drivers/base/Kconfig | 14 ++++----------
fs/namespace.c | 14 ++++++++++++++
init/main.c | 15 +++++++++------
3 files changed, 27 insertions(+), 16 deletions(-)
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index f046d21..97352d4 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/fs/namespace.c b/fs/namespace.c
index f8893dc..06057d7 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2417,7 +2417,21 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
err = -EBUSY;
if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
path->mnt->mnt_root == path->dentry)
+ {
+ if (IS_ENABLED(CONFIG_DEVTMPFS_MOUNT) &&
+ !strcmp(path->mnt->mnt_sb->s_type->name, "devtmpfs"))
+ {
+ /* Debian's kernel config enables DEVTMPFS_MOUNT, then
+ its initramfs setup script tries to mount devtmpfs
+ again, and if the second mount-over-itself fails
+ the script overmounts a tmpfs on /dev to hide the
+ existing contents, then boot fails with empty /dev. */
+ printk(KERN_WARNING "Debian bug workaround for devtmpfs overmount.");
+
+ err = 0;
+ }
goto unlock;
+ }
err = -EINVAL;
if (d_is_symlink(newmnt->mnt.mnt_root))
diff --git a/init/main.c b/init/main.c
index 0ee9c686..0d8e5ec 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1065,12 +1065,6 @@ 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
@@ -1082,8 +1076,17 @@ 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
Le 14/09/2017 à 01:51, Rob Landley a écrit :
> From: Rob Landley <[email protected]>
>
> 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 ?
Why should a Debian bug be fixed by a workaround in the mainline kernel ?
>
> Signed-off-by: Rob Landley <[email protected]>
> ---
>
> v2 discussion: http://lkml.iu.edu/hypermail/linux/kernel/1705.2/05611.html
>
> drivers/base/Kconfig | 14 ++++----------
> fs/namespace.c | 14 ++++++++++++++
> init/main.c | 15 +++++++++------
> 3 files changed, 27 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index f046d21..97352d4 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.
Why modifying the initial text ?
Why talking about rescue mode only, whereas this feature mainly concerns
the standard mode.
>
> config STANDALONE
> bool "Select only drivers that don't need compile-time external firmware"
> diff --git a/fs/namespace.c b/fs/namespace.c
> index f8893dc..06057d7 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2417,7 +2417,21 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
> err = -EBUSY;
> if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
> path->mnt->mnt_root == path->dentry)
> + {
> + if (IS_ENABLED(CONFIG_DEVTMPFS_MOUNT) &&
> + !strcmp(path->mnt->mnt_sb->s_type->name, "devtmpfs"))
> + {
> + /* Debian's kernel config enables DEVTMPFS_MOUNT, then
> + its initramfs setup script tries to mount devtmpfs
> + again, and if the second mount-over-itself fails
> + the script overmounts a tmpfs on /dev to hide the
> + existing contents, then boot fails with empty /dev. */
Does it matter for the kernel code what Debian's kernel config does ?
> + printk(KERN_WARNING "Debian bug workaround for devtmpfs overmount.");
Is this log message worth it when this modification goes in mainline
kernel ?
If so, pr_err() should be used instead.
> +
> + err = 0;
> + }
> goto unlock;
> + }
>
> err = -EINVAL;
> if (d_is_symlink(newmnt->mnt.mnt_root))
> diff --git a/init/main.c b/init/main.c
> index 0ee9c686..0d8e5ec 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1065,12 +1065,6 @@ 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
> @@ -1082,8 +1076,17 @@ 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);
Why not, but couldn't we also expect the initramfs to already contains
that mountpoint ?
> + 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
>
Christophe
On Wed, Sep 13, 2017 at 06:51:25PM -0500, Rob Landley wrote:
> From: Rob Landley <[email protected]>
>
> Make initramfs honor CONFIG_DEVTMPFS_MOUNT, and move
> /dev/console open after devtmpfs mount.
>
> Add workaround for Debian bug that was copied by Ubuntu.
>
> Signed-off-by: Rob Landley <[email protected]>
> ---
>
> v2 discussion: http://lkml.iu.edu/hypermail/linux/kernel/1705.2/05611.html
>
> drivers/base/Kconfig | 14 ++++----------
> fs/namespace.c | 14 ++++++++++++++
> init/main.c | 15 +++++++++------
> 3 files changed, 27 insertions(+), 16 deletions(-)
Always run scripts/checkpatch.pl so you don't get grumpy emails from
reviewers telling you to run scripts/checkpatch.pl... telling you to run
scripts/checkpatch.pl... telling you to run scripts/checkpatch.pl...
telling you to run scripts/checkpatch.pl...
On 09/14/2017 04:17 AM, Christophe LEROY wrote:
> Le 14/09/2017 à 01:51, Rob Landley a écrit :
>> From: Rob Landley <[email protected]>
>>
>> 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
On Sat, 16 Sep 2017, Rob Landley wrote:
> So, I added a workaround with a printk in hopes of embarassing them into
> someday fixing it.
Oh, it will be fixed in Debian alright. I am just waiting the issue to
settle a bit to file the bug reports, or maybe even send in the Debian
patches myself (note that I am not responsible for the code in question,
so I am not wearing a brown paperbag at this time). Even if I didn't do
it, there are several other Debian Developers reading LKML that could do
it (provided they noticed this specific thread and are aware of the
situation) :p
I can even push for the fixes to be accepted into the stable and
oldstable branches of Debian, but that can take anything from a few
weeks to several months, due to the way our stable releases work. But
it would eventually happen.
Whether such fixes will ever make it to LTS branches, especially
Ubuntu's, *that* I don't know.
--
Henrique Holschuh
On 09/17/2017 08:51 AM, Henrique de Moraes Holschuh wrote:
> On Sat, 16 Sep 2017, Rob Landley wrote:
>> So, I added a workaround with a printk in hopes of embarassing them into
>> someday fixing it.
>
> Oh, it will be fixed in Debian alright.
Cool!
But part of the problem is people upgrade the kernel on existing
deployed root filesystems, some of which are a fork off of a fork off of
debian, so we won't exhaust the broken userspace for probably a couple
years.
I'd put it in feature-removal-schedule.txt but Linus zapped that, so...
> I am just waiting the issue to
> settle a bit to file the bug reports, or maybe even send in the Debian
> patches myself (note that I am not responsible for the code in question,
> so I am not wearing a brown paperbag at this time). Even if I didn't do
> it, there are several other Debian Developers reading LKML that could do
> it (provided they noticed this specific thread and are aware of the
> situation) :p
There was a previous thread last merge window they didn't notice. I was
hoping the warning would be obvious enough. :)
> I can even push for the fixes to be accepted into the stable and
> oldstable branches of Debian, but that can take anything from a few
> weeks to several months, due to the way our stable releases work. But
> it would eventually happen.
>
> Whether such fixes will ever make it to LTS branches, especially
> Ubuntu's, *that* I don't know.
I have no idea what that powerpc system was, the guy didn't say...
Rob
Rob Landley <[email protected]> writes:
> On 09/14/2017 04:17 AM, Christophe LEROY wrote:
>> Le 14/09/2017 à 01:51, Rob Landley a écrit :
>>> From: Rob Landley <[email protected]>
>>>
>>> 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. :)
I'm still here. And I'm still right :)
No one wants their system to stop booting because of this obscure
functionality.
Just put it behind a new config option which defaults off. No
workarounds required, no broken systems, no long email threads required.
cheers