[PATCH -next v2 0/3] cleanup of devtmpfs_*_node()

[PATCH -next v2 0/3] cleanup of devtmpfs_*_node()

[Longlong Xia]

In one test, when modprobe zram, no zram device was found in the /dev. 
But don't see any errors printed in jouranls/dmesg. Later we found out 
that the reason was that device_add() did not check its return value when
calling devtmpfs_create_node().

The test steps:
1. Set the SElinux label of /dev to user_home_t 
2. modprobe zram num_devices=1000

v1 -> v2:
- New patch 1 to add error handling for devtmpfs_create_node().
- use dev_err() to replace pr_err_ratelimited in [2].
- only remove return value of devtmpfs_delete_node() in [3].

Longlong Xia (3):
  driver core: add error handling for devtmpfs_create_node()
  devtmpfs: add debug info to handle()
  devtmpfs: remove return value of devtmpfs_delete_node()

 drivers/base/base.h     |  4 ++--
 drivers/base/core.c     |  6 +++++-
 drivers/base/devtmpfs.c | 20 ++++++++++++++------
 3 files changed, 21 insertions(+), 9 deletions(-)

-- 
2.25.1

[PATCH -next v2 1/3] driver core: add error handling for devtmpfs_create_node()

[Longlong Xia]

In some cases, devtmpfs_create_node() can return error value.
So, make use of it.

Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
---
 drivers/base/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 7dab705f2937..aaa3088e5456 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3405,7 +3405,9 @@ int device_add(struct device *dev)
 		if (error)
 			goto SysEntryError;
 
-		devtmpfs_create_node(dev);
+		error = devtmpfs_create_node(dev);
+		if (error)
+			goto DevtmpfsError;
 	}
 
 	/* Notify clients of device addition.  This call must come
@@ -3461,6 +3463,8 @@ int device_add(struct device *dev)
 done:
 	put_device(dev);
 	return error;
+ DevtmpfsError:
+	device_remove_sys_dev_entry(dev);
  SysEntryError:
 	if (MAJOR(dev->devt))
 		device_remove_file(dev, &dev_attr_dev);
-- 
2.25.1

Re: [PATCH -next v2 1/3] driver core: add error handling for devtmpfs_create_node()

[Nathan Chancellor]

Hi Longlong,

On Fri, Feb 10, 2023 at 09:54:42AM +0000, Longlong Xia wrote:
> In some cases, devtmpfs_create_node() can return error value.
> So, make use of it.
> 
> Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
> ---
>  drivers/base/core.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 7dab705f2937..aaa3088e5456 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3405,7 +3405,9 @@ int device_add(struct device *dev)
>  		if (error)
>  			goto SysEntryError;
>  
> -		devtmpfs_create_node(dev);
> +		error = devtmpfs_create_node(dev);
> +		if (error)
> +			goto DevtmpfsError;
>  	}
>  
>  	/* Notify clients of device addition.  This call must come
> @@ -3461,6 +3463,8 @@ int device_add(struct device *dev)
>  done:
>  	put_device(dev);
>  	return error;
> + DevtmpfsError:
> +	device_remove_sys_dev_entry(dev);
>   SysEntryError:
>  	if (MAJOR(dev->devt))
>  		device_remove_file(dev, &dev_attr_dev);
> -- 
> 2.25.1
> 

After this change in -next as commit 31b4b6730fd4 ("driver core: add
error handling for devtmpfs_create_node()"), my test machines failed to
boot after the rootfs could not be mounted. I added some logging to see
which device was failing, which triggers a few times with the exact same
message:

  device: 'btrfs-control': devtmpfs_create_node() failed, err = -17

with -17 being -EEXIST. I am not sure why this device is getting
registered more than once, it appears to occur during module insertion
though, as I am able to get to systemd starting within the initrd.

Should this particular return value be downgraded to a warning so that
the device still loads or should the driver be fixed? I have cc'd the
btrfs mailing list, in case they have any input.

Cheers,
Nathan

Re: [PATCH -next v2 1/3] driver core: add error handling for devtmpfs_create_node()

[Nathan Chancellor]

On Mon, Feb 13, 2023 at 05:14:27PM -0700, Nathan Chancellor wrote:
> Hi Longlong,
> 
> On Fri, Feb 10, 2023 at 09:54:42AM +0000, Longlong Xia wrote:
> > In some cases, devtmpfs_create_node() can return error value.
> > So, make use of it.
> > 
> > Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
> > ---
> >  drivers/base/core.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 7dab705f2937..aaa3088e5456 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -3405,7 +3405,9 @@ int device_add(struct device *dev)
> >  		if (error)
> >  			goto SysEntryError;
> >  
> > -		devtmpfs_create_node(dev);
> > +		error = devtmpfs_create_node(dev);
> > +		if (error)
> > +			goto DevtmpfsError;
> >  	}
> >  
> >  	/* Notify clients of device addition.  This call must come
> > @@ -3461,6 +3463,8 @@ int device_add(struct device *dev)
> >  done:
> >  	put_device(dev);
> >  	return error;
> > + DevtmpfsError:
> > +	device_remove_sys_dev_entry(dev);
> >   SysEntryError:
> >  	if (MAJOR(dev->devt))
> >  		device_remove_file(dev, &dev_attr_dev);
> > -- 
> > 2.25.1
> > 
> 
> After this change in -next as commit 31b4b6730fd4 ("driver core: add
> error handling for devtmpfs_create_node()"), my test machines failed to
> boot after the rootfs could not be mounted. I added some logging to see
> which device was failing, which triggers a few times with the exact same
> message:
> 
>   device: 'btrfs-control': devtmpfs_create_node() failed, err = -17
> 
> with -17 being -EEXIST. I am not sure why this device is getting
> registered more than once, it appears to occur during module insertion
> though, as I am able to get to systemd starting within the initrd.
> 
> Should this particular return value be downgraded to a warning so that
> the device still loads or should the driver be fixed? I have cc'd the
> btrfs mailing list, in case they have any input.

Apologies, I see now that the second patch in this series is logging for
this, sorry for not using or noticing that sooner.

I am now looking at some of my other test machines and I see messages
similar to the one above for other devices:

[   16.268685] sound timer: failed to create snd/timer, ret = -17
[   16.274666] ALSA: unable to register timer device (-17)
[   16.500253] sound timer: failed to create snd/timer, ret = -17
[   16.506124] ALSA: unable to register timer device (-17)

[   18.273067] misc rfkill: failed to create rfkill, ret = -17
[   18.464836] misc rfkill: failed to create rfkill, ret = -17
[   19.366149] misc tun: failed to create net/tun, ret = -17
[   19.371613] tun: Can't register misc device 200
[   19.552362] misc tun: failed to create net/tun, ret = -17
[   19.557839] tun: Can't register misc device 200
[   23.124993] misc tun: failed to create net/tun, ret = -17
[   23.130460] tun: Can't register misc device 200
[   23.299267] misc tun: failed to create net/tun, ret = -17
[   23.299319] tun: Can't register misc device 200
[   27.050363] misc tun: failed to create net/tun, ret = -17
[   27.055824] tun: Can't register misc device 200
[   27.181496] misc tun: failed to create net/tun, ret = -17

So it seems like this is not a btrfs specific problem?

Cheers,
Nathan

Re: [PATCH -next v2 1/3] driver core: add error handling for devtmpfs_create_node()

[Greg KH]

On Mon, Feb 13, 2023 at 05:33:06PM -0700, Nathan Chancellor wrote:
> On Mon, Feb 13, 2023 at 05:14:27PM -0700, Nathan Chancellor wrote:
> > Hi Longlong,
> > 
> > On Fri, Feb 10, 2023 at 09:54:42AM +0000, Longlong Xia wrote:
> > > In some cases, devtmpfs_create_node() can return error value.
> > > So, make use of it.
> > > 
> > > Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
> > > ---
> > >  drivers/base/core.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > index 7dab705f2937..aaa3088e5456 100644
> > > --- a/drivers/base/core.c
> > > +++ b/drivers/base/core.c
> > > @@ -3405,7 +3405,9 @@ int device_add(struct device *dev)
> > >  		if (error)
> > >  			goto SysEntryError;
> > >  
> > > -		devtmpfs_create_node(dev);
> > > +		error = devtmpfs_create_node(dev);
> > > +		if (error)
> > > +			goto DevtmpfsError;
> > >  	}
> > >  
> > >  	/* Notify clients of device addition.  This call must come
> > > @@ -3461,6 +3463,8 @@ int device_add(struct device *dev)
> > >  done:
> > >  	put_device(dev);
> > >  	return error;
> > > + DevtmpfsError:
> > > +	device_remove_sys_dev_entry(dev);
> > >   SysEntryError:
> > >  	if (MAJOR(dev->devt))
> > >  		device_remove_file(dev, &dev_attr_dev);
> > > -- 
> > > 2.25.1
> > > 
> > 
> > After this change in -next as commit 31b4b6730fd4 ("driver core: add
> > error handling for devtmpfs_create_node()"), my test machines failed to
> > boot after the rootfs could not be mounted. I added some logging to see
> > which device was failing, which triggers a few times with the exact same
> > message:
> > 
> >   device: 'btrfs-control': devtmpfs_create_node() failed, err = -17
> > 
> > with -17 being -EEXIST. I am not sure why this device is getting
> > registered more than once, it appears to occur during module insertion
> > though, as I am able to get to systemd starting within the initrd.
> > 
> > Should this particular return value be downgraded to a warning so that
> > the device still loads or should the driver be fixed? I have cc'd the
> > btrfs mailing list, in case they have any input.
> 
> Apologies, I see now that the second patch in this series is logging for
> this, sorry for not using or noticing that sooner.
> 
> I am now looking at some of my other test machines and I see messages
> similar to the one above for other devices:
> 
> [   16.268685] sound timer: failed to create snd/timer, ret = -17
> [   16.274666] ALSA: unable to register timer device (-17)
> [   16.500253] sound timer: failed to create snd/timer, ret = -17
> [   16.506124] ALSA: unable to register timer device (-17)
> 
> [   18.273067] misc rfkill: failed to create rfkill, ret = -17
> [   18.464836] misc rfkill: failed to create rfkill, ret = -17
> [   19.366149] misc tun: failed to create net/tun, ret = -17
> [   19.371613] tun: Can't register misc device 200
> [   19.552362] misc tun: failed to create net/tun, ret = -17
> [   19.557839] tun: Can't register misc device 200
> [   23.124993] misc tun: failed to create net/tun, ret = -17
> [   23.130460] tun: Can't register misc device 200
> [   23.299267] misc tun: failed to create net/tun, ret = -17
> [   23.299319] tun: Can't register misc device 200
> [   27.050363] misc tun: failed to create net/tun, ret = -17
> [   27.055824] tun: Can't register misc device 200
> [   27.181496] misc tun: failed to create net/tun, ret = -17
> 
> So it seems like this is not a btrfs specific problem?

Ok, let me go revert the series for now.  Longlong, please feel free to
resubmit after testing this a bit better.

thanks,

greg k-h

[PATCH -next v2 2/3] devtmpfs: add debug info to handle()

[Longlong Xia]

Because handle() is the core function for processing devtmpfs requests,
Let's add some debug info in handle() to help users know why failed.

Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
---
 drivers/base/devtmpfs.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index ae72d4ba8547..7789b7be4ee5 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -389,10 +389,18 @@ static __initdata DECLARE_COMPLETION(setup_done);
 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
 		  struct device *dev)
 {
+	int ret;
+
 	if (mode)
-		return handle_create(name, mode, uid, gid, dev);
+		ret = handle_create(name, mode, uid, gid, dev);
 	else
-		return handle_remove(name, dev);
+		ret = handle_remove(name, dev);
+
+	if (ret)
+		dev_err(dev, "failed to %s %s, ret = %d\n",
+			mode ? "create" : "remove", name, ret);
+
+	return ret;
 }
 
 static void __noreturn devtmpfs_work_loop(void)
-- 
2.25.1

[PATCH -next v2 3/3] devtmpfs: remove return value of devtmpfs_delete_node()

[Longlong Xia]

The only caller of device_del() does not check the return value. And
there's nothing we can do when cleaning things up on a remove path.
Let's make it a void function.

Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
---
 drivers/base/base.h     | 4 ++--
 drivers/base/devtmpfs.c | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 0e806f641079..f7996bf8d28b 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -201,10 +201,10 @@ void device_pm_move_to_tail(struct device *dev);
 
 #ifdef CONFIG_DEVTMPFS
 int devtmpfs_create_node(struct device *dev);
-int devtmpfs_delete_node(struct device *dev);
+void devtmpfs_delete_node(struct device *dev);
 #else
 static inline int devtmpfs_create_node(struct device *dev) { return 0; }
-static inline int devtmpfs_delete_node(struct device *dev) { return 0; }
+static inline void devtmpfs_delete_node(struct device *dev) { return 0; }
 #endif
 
 void software_node_notify(struct device *dev);
diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 7789b7be4ee5..e5c4d3e98ec9 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -147,22 +147,22 @@ int devtmpfs_create_node(struct device *dev)
 	return devtmpfs_submit_req(&req, tmp);
 }
 
-int devtmpfs_delete_node(struct device *dev)
+void devtmpfs_delete_node(struct device *dev)
 {
 	const char *tmp = NULL;
 	struct req req;
 
 	if (!thread)
-		return 0;
+		return;
 
 	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
 	if (!req.name)
-		return -ENOMEM;
+		return;
 
 	req.mode = 0;
 	req.dev = dev;
 
-	return devtmpfs_submit_req(&req, tmp);
+	devtmpfs_submit_req(&req, tmp);
 }
 
 static int dev_mkdir(const char *name, umode_t mode)
-- 
2.25.1

Re: [PATCH -next v2 0/3] cleanup of devtmpfs_*_node()

[Greg KH]

On Fri, Feb 10, 2023 at 09:54:41AM +0000, Longlong Xia wrote:
> In one test, when modprobe zram, no zram device was found in the /dev. 
> But don't see any errors printed in jouranls/dmesg. Later we found out 
> that the reason was that device_add() did not check its return value when
> calling devtmpfs_create_node().
> 
> The test steps:
> 1. Set the SElinux label of /dev to user_home_t 
> 2. modprobe zram num_devices=1000
> 
> v1 -> v2:
> - New patch 1 to add error handling for devtmpfs_create_node().
> - use dev_err() to replace pr_err_ratelimited in [2].
> - only remove return value of devtmpfs_delete_node() in [3].
> 
> Longlong Xia (3):
>   driver core: add error handling for devtmpfs_create_node()
>   devtmpfs: add debug info to handle()
>   devtmpfs: remove return value of devtmpfs_delete_node()
> 
>  drivers/base/base.h     |  4 ++--
>  drivers/base/core.c     |  6 +++++-
>  drivers/base/devtmpfs.c | 20 ++++++++++++++------
>  3 files changed, 21 insertions(+), 9 deletions(-)
> 
> -- 
> 2.25.1
> 

Thanks for the quick resend, nice work, all now queued up!

greg k-h