Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-21 Thread Michael Ellerman 
Rob Landley  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 
>>>
>>> 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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-21 Thread Michael Ellerman 
Rob Landley  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 
>>>
>>> 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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-19 Thread Rob Landley 
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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-19 Thread Rob Landley 
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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-17 Thread Henrique de Moraes Holschuh 
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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-17 Thread Henrique de Moraes Holschuh 
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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-16 Thread Rob Landley 
On 09/14/2017 04:17 AM, Christophe LEROY wrote:
> Le 14/09/2017 à 01:51, Rob Landley a écrit :
>> From: Rob Landley 
>>
>> 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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-16 Thread Rob Landley 
On 09/14/2017 04:17 AM, Christophe LEROY wrote:
> Le 14/09/2017 à 01:51, Rob Landley a écrit :
>> From: Rob Landley 
>>
>> 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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-14 Thread Greg KH 
On Wed, Sep 13, 2017 at 06:51:25PM -0500, Rob Landley wrote:
> From: Rob Landley 
> 
> 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 
> ---
> 
> 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...

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-14 Thread Greg KH 
On Wed, Sep 13, 2017 at 06:51:25PM -0500, Rob Landley wrote:
> From: Rob Landley 
> 
> 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 
> ---
> 
> 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...

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-14 Thread Christophe LEROY 

Le 14/09/2017 à 01:51, Rob Landley a écrit :

From: Rob Landley 

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 
---

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

Re: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-14 Thread Christophe LEROY 

Le 14/09/2017 à 01:51, Rob Landley a écrit :

From: Rob Landley 

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 
---

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

[PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-13 Thread Rob Landley 
From: Rob Landley 

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 
---

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

[PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

2017-09-13 Thread Rob Landley 
From: Rob Landley 

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 
---

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