[PATCH 0/2 v2] cpu: fix leaks and udev race in register_cpu()

[PATCH 0/2 v2] cpu: fix leaks and udev race in register_cpu()

[Igor Mammedov]

1. move "crash_notes" and "crash_notes_size" to static attributes to
guarantee that it's destroyed with CPU on unregister.

2. fixes race between hotplugged CPU and onlining it via udev,
described at https://lkml.org/lkml/2012/4/30/193

Igor Mammedov (2):
  cpu: fix "crash_notes" and "crash_notes_size" leaks in register_cpu()
  cpu: make sure that cpu/online file created before KOBJ_ADD is
    emitted

 drivers/base/cpu.c |   59 ++++++++++++++++++++++++++++++++++-----------------
 1 files changed, 39 insertions(+), 20 deletions(-)

[PATCH 1/2] cpu: fix "crash_notes" and "crash_notes_size" leaks in register_cpu()

[Igor Mammedov]

"crash_notes" and "crash_notes_size" are dynamically created
with device_create_file() but aren't deleted anywhere.
Define "crash_notes" and "crash_notes_size" statically via
attribute groups so that device_register would create them
automatically and files would be destroyed when CPU is destroyed.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 drivers/base/cpu.c |   25 ++++++++++++++++++-------
 1 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 3d48fc8..8f9e264 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -164,7 +164,24 @@ static ssize_t show_crash_notes_size(struct device *dev,
 	return rc;
 }
 static DEVICE_ATTR(crash_notes_size, 0400, show_crash_notes_size, NULL);
+
+static struct attribute *crash_note_cpu_attrs[] = {
+	&dev_attr_crash_notes.attr,
+	&dev_attr_crash_notes_size.attr,
+	NULL
+};
+
+static struct attribute_group crash_note_cpu_attr_group = {
+	.attrs = crash_note_cpu_attrs,
+};
+#endif
+
+static const struct attribute_group *common_cpu_attr_groups[] = {
+#ifdef CONFIG_KEXEC
+	&crash_note_cpu_attr_group,
 #endif
+	NULL
+};
 
 /*
  * Print cpu online, possible, present, and system maps
@@ -280,6 +297,7 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
 #ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
 	cpu->dev.bus->uevent = arch_cpu_uevent;
 #endif
+	cpu->dev.groups = common_cpu_attr_groups;
 	error = device_register(&cpu->dev);
 	if (!error && cpu->hotpluggable)
 		register_cpu_control(cpu);
@@ -288,13 +306,6 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
 	if (!error)
 		register_cpu_under_node(num, cpu_to_node(num));
 
-#ifdef CONFIG_KEXEC
-	if (!error)
-		error = device_create_file(&cpu->dev, &dev_attr_crash_notes);
-	if (!error)
-		error = device_create_file(&cpu->dev,
-					   &dev_attr_crash_notes_size);
-#endif
 	return error;
 }
 
-- 
1.7.1

[PATCH 2/2] cpu: make sure that cpu/online file created before KOBJ_ADD is emitted

[Igor Mammedov]

It fixes race between udev and hotplugged CPU registration by defining
"online" attribute statically, so that device_add() would create it
before notifying udev about new CPU.

Original issue report is at https://lkml.org/lkml/2012/4/30/198
"
> On Mon, Apr 30, 2012 at 11:36:23AM -0400, Konrad Rzeszutek Wilk wrote:
> > Hey Greg,
> >
> > Hoping you can help with some guidance on how to fix this.
> >
> > The issue is with CPU hotplug is that when a CPU goes up
> > it calls 'arch_register_cpu' which eventually calls
> > register_cpu. That function does these two things:
> >
> > 251         error = device_register(&cpu->dev);
> > 252         if (!error && cpu->hotpluggable)
> > 253                 register_cpu_control(cpu);
> >
> > and the device_register creates a nice little SysFS directory:
> >
> > /sys/devices/system/cpu/cpu2/ which at line 251 has the 'add' attribute
> > but no 'online' attribute. udev then tries to echo 1 to the 'online'
> > and it we get:
> > udevd-work[2421]: error opening ATTR{/sys/devices/system/cpu/cpu2/online} for writing: No such file or directory
> >
> > Line 253 creates said 'online' and at that time udev [or the system admin]
> > can write 1 to 'online' and the CPU goes up.
> >
> > So .. any thoughts? Is there some way to inhibit from uevent being sent
> > until line 253 has run?
"

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 drivers/base/cpu.c |   34 +++++++++++++++++++++-------------
 1 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 8f9e264..c377673 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -85,18 +85,21 @@ static ssize_t __ref store_online(struct device *dev,
 }
 static DEVICE_ATTR(online, 0644, show_online, store_online);
 
-static void __cpuinit register_cpu_control(struct cpu *cpu)
-{
-	device_create_file(&cpu->dev, &dev_attr_online);
-}
+static struct attribute *hotplug_cpu_attrs[] = {
+	&dev_attr_online.attr,
+	NULL
+};
+
+static struct attribute_group hotplug_cpu_attr_group = {
+	.attrs = hotplug_cpu_attrs,
+};
+
 void unregister_cpu(struct cpu *cpu)
 {
 	int logical_cpu = cpu->dev.id;
 
 	unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
 
-	device_remove_file(&cpu->dev, &dev_attr_online);
-
 	device_unregister(&cpu->dev);
 	per_cpu(cpu_sys_devices, logical_cpu) = NULL;
 	return;
@@ -122,11 +125,6 @@ static ssize_t cpu_release_store(struct device *dev,
 static DEVICE_ATTR(probe, S_IWUSR, NULL, cpu_probe_store);
 static DEVICE_ATTR(release, S_IWUSR, NULL, cpu_release_store);
 #endif /* CONFIG_ARCH_CPU_PROBE_RELEASE */
-
-#else /* ... !CONFIG_HOTPLUG_CPU */
-static inline void register_cpu_control(struct cpu *cpu)
-{
-}
 #endif /* CONFIG_HOTPLUG_CPU */
 
 #ifdef CONFIG_KEXEC
@@ -183,6 +181,16 @@ static const struct attribute_group *common_cpu_attr_groups[] = {
 	NULL
 };
 
+static const struct attribute_group *hotplugable_cpu_attr_groups[] = {
+#ifdef CONFIG_KEXEC
+	&crash_note_cpu_attr_group,
+#endif
+#ifdef CONFIG_HOTPLUG_CPU
+	&hotplug_cpu_attr_group,
+#endif
+	NULL
+};
+
 /*
  * Print cpu online, possible, present, and system maps
  */
@@ -298,9 +306,9 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
 	cpu->dev.bus->uevent = arch_cpu_uevent;
 #endif
 	cpu->dev.groups = common_cpu_attr_groups;
+	if (cpu->hotpluggable)
+		cpu->dev.groups = hotplugable_cpu_attr_groups;
 	error = device_register(&cpu->dev);
-	if (!error && cpu->hotpluggable)
-		register_cpu_control(cpu);
 	if (!error)
 		per_cpu(cpu_sys_devices, num) = &cpu->dev;
 	if (!error)
-- 
1.7.1

Re: [PATCH 0/2 v2] cpu: fix leaks and udev race in register_cpu()

[Greg KH]

On Tue, May 14, 2013 at 04:46:05PM +0200, Igor Mammedov wrote:
> 1. move "crash_notes" and "crash_notes_size" to static attributes to
> guarantee that it's destroyed with CPU on unregister.
> 
> 2. fixes race between hotplugged CPU and onlining it via udev,
> described at https://lkml.org/lkml/2012/4/30/193
> 
> Igor Mammedov (2):
>   cpu: fix "crash_notes" and "crash_notes_size" leaks in register_cpu()
>   cpu: make sure that cpu/online file created before KOBJ_ADD is
>     emitted
> 
>  drivers/base/cpu.c |   59 ++++++++++++++++++++++++++++++++++-----------------
>  1 files changed, 39 insertions(+), 20 deletions(-)

Nice, give me a few days to catch up with my patch queue, and I'll apply
this.

greg k-h

Re: udev races with 'arch_register_cpu' to write 1 to /sys/devices/system/cpu/cpu1/online (which is not yet created)

[Konrad Rzeszutek Wilk]

On Fri, May 10, 2013 at 06:34:34PM +0200, Igor Mammedov wrote:
> >On Mon, Apr 30, 2012 at 11:51:49AM -0400, Greg KH wrote:
> >> On Mon, Apr 30, 2012 at 11:50:18AM -0400, Greg KH wrote:
> >> > On Mon, Apr 30, 2012 at 11:36:23AM -0400, Konrad Rzeszutek Wilk wrote:
> >> > > Hey Greg,
> >> > > 
> >> > > Hoping you can help with some guidance on how to fix this.
> >> > > 
> >> > > The issue is with CPU hotplug is that when a CPU goes up
> >> > > it calls 'arch_register_cpu' which eventually calls
> >> > > register_cpu. That function does these two things:
> >> > > 
> >> > > 251         error = device_register(&cpu->dev);
> >> > > 252         if (!error && cpu->hotpluggable)
> >> > > 253                 register_cpu_control(cpu);
> >> > > 
> >> > > and the device_register creates a nice little SysFS directory:
> >> > > 
> >> > > /sys/devices/system/cpu/cpu2/ which at line 251 has the 'add' attribute
> >> > > but no 'online' attribute. udev then tries to echo 1 to the 'online'
> >> > > and it we get:
> >> > > udevd-work[2421]: error opening ATTR{/sys/devices/system/cpu/cpu2/online} for writing: No such file or directory
> >> > > 
> >> > > Line 253 creates said 'online' and at that time udev [or the system admin]
> >> > > can write 1 to 'online' and the CPU goes up.
> >> > > 
> >> > > So .. any thoughts? Is there some way to inhibit from uevent being sent
> >> > > until line 253 has run?
> >> > 
> >> > Yes.
> >> 
> >> Oh, I imagine you want to know _how_ to do it too, right?  (sorry, I
> >> couldn't resist...)
> >
> >Heh.
> >> 
> >> Make this a default attribute of the cpu device, and then it will be
> >> created by the driver core before the uevent is sent to userspace.
> >> That's what you are supposed to do in the first place, adding files "by
> >> hand" is wrong, for this very reason.
> >
> >OK, will prep up a patch shortly.
> 
> Hello Konrad,
> 
> Is there a posted/accepted patch or idea was dropped?

Hey Igor,

CC-ing here Chuck here who is looking at that. My recollection (and Chuck please
correct me if I am wrong) is that the idea Greg outlined won't work very well.
The reason is that making 'online' an attribute of 'struct dev' means that:
 1) A lot of SysFS attributes that have no notion of online/offline (say ISA bus)
    will now have.
 2) The default action item (so function) to do something based on writting/reading
    from 'online' will have to be overridden by the driver using it. Which means
    another race - we can create an SysFS attribute but the default points to something
    that does nothing.

Chuck, does that sound right?
> 
> 

[PATCH 2/2] cpu: make sure that cpu/online file created before KOBJ_ADD is emitted

[Igor Mammedov]

Fixes race between udev and hotplugged CPU registration, described at
https://lkml.org/lkml/2012/4/30/198
by defining "online" attribute statically so that device_add() would
create it before notifying udev about new CPU.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 drivers/base/cpu.c |   34 +++++++++++++++++++++-------------
 1 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 02e4d73..6578030 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -64,18 +64,21 @@ static ssize_t __ref store_online(struct device *dev,
 }
 static DEVICE_ATTR(online, 0644, show_online, store_online);
 
-static void __cpuinit register_cpu_control(struct cpu *cpu)
-{
-	device_create_file(&cpu->dev, &dev_attr_online);
-}
+static struct attribute *hotplug_cpu_attrs[] = {
+	&dev_attr_online.attr,
+	NULL
+};
+
+static struct attribute_group hotplug_cpu_attr_group = {
+	.attrs = hotplug_cpu_attrs,
+};
+
 void unregister_cpu(struct cpu *cpu)
 {
 	int logical_cpu = cpu->dev.id;
 
 	unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
 
-	device_remove_file(&cpu->dev, &dev_attr_online);
-
 	device_unregister(&cpu->dev);
 	per_cpu(cpu_sys_devices, logical_cpu) = NULL;
 	return;
@@ -101,11 +104,6 @@ static ssize_t cpu_release_store(struct device *dev,
 static DEVICE_ATTR(probe, S_IWUSR, NULL, cpu_probe_store);
 static DEVICE_ATTR(release, S_IWUSR, NULL, cpu_release_store);
 #endif /* CONFIG_ARCH_CPU_PROBE_RELEASE */
-
-#else /* ... !CONFIG_HOTPLUG_CPU */
-static inline void register_cpu_control(struct cpu *cpu)
-{
-}
 #endif /* CONFIG_HOTPLUG_CPU */
 
 #ifdef CONFIG_KEXEC
@@ -150,6 +148,16 @@ static const struct attribute_group *common_cpu_attr_groups[] = {
 	NULL
 };
 
+static const struct attribute_group *hotplugable_cpu_attr_groups[] = {
+#ifdef CONFIG_KEXEC
+	&crash_note_cpu_attr_group,
+#endif
+#ifdef CONFIG_HOTPLUG_CPU
+	&hotplug_cpu_attr_group,
+#endif
+	NULL
+};
+
 /*
  * Print cpu online, possible, present, and system maps
  */
@@ -265,9 +273,9 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
 	cpu->dev.bus->uevent = arch_cpu_uevent;
 #endif
 	cpu->dev.groups = common_cpu_attr_groups;
+	if (cpu->hotpluggable)
+		cpu->dev.groups = hotplugable_cpu_attr_groups;
 	error = device_register(&cpu->dev);
-	if (!error && cpu->hotpluggable)
-		register_cpu_control(cpu);
 	if (!error)
 		per_cpu(cpu_sys_devices, num) = &cpu->dev;
 	if (!error)
-- 
1.7.1

Re: [PATCH 2/2] cpu: make sure that cpu/online file created before KOBJ_ADD is emitted

[Konrad Rzeszutek Wilk]

On Tue, May 14, 2013 at 12:05:32AM +0200, Igor Mammedov wrote:
> Fixes race between udev and hotplugged CPU registration, described at
> https://lkml.org/lkml/2012/4/30/198

It would be better if you copy-n-pasted the contents of that URL in here.
> by defining "online" attribute statically so that device_add() would
> create it before notifying udev about new CPU.

> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  drivers/base/cpu.c |   34 +++++++++++++++++++++-------------
>  1 files changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 02e4d73..6578030 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -64,18 +64,21 @@ static ssize_t __ref store_online(struct device *dev,
>  }
>  static DEVICE_ATTR(online, 0644, show_online, store_online);
>  
> -static void __cpuinit register_cpu_control(struct cpu *cpu)
> -{
> -	device_create_file(&cpu->dev, &dev_attr_online);
> -}
> +static struct attribute *hotplug_cpu_attrs[] = {
> +	&dev_attr_online.attr,
> +	NULL
> +};
> +
> +static struct attribute_group hotplug_cpu_attr_group = {
> +	.attrs = hotplug_cpu_attrs,
> +};
> +
>  void unregister_cpu(struct cpu *cpu)
>  {
>  	int logical_cpu = cpu->dev.id;
>  
>  	unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
>  
> -	device_remove_file(&cpu->dev, &dev_attr_online);
> -
>  	device_unregister(&cpu->dev);
>  	per_cpu(cpu_sys_devices, logical_cpu) = NULL;
>  	return;
> @@ -101,11 +104,6 @@ static ssize_t cpu_release_store(struct device *dev,
>  static DEVICE_ATTR(probe, S_IWUSR, NULL, cpu_probe_store);
>  static DEVICE_ATTR(release, S_IWUSR, NULL, cpu_release_store);
>  #endif /* CONFIG_ARCH_CPU_PROBE_RELEASE */
> -
> -#else /* ... !CONFIG_HOTPLUG_CPU */
> -static inline void register_cpu_control(struct cpu *cpu)
> -{
> -}
>  #endif /* CONFIG_HOTPLUG_CPU */
>  
>  #ifdef CONFIG_KEXEC
> @@ -150,6 +148,16 @@ static const struct attribute_group *common_cpu_attr_groups[] = {
>  	NULL
>  };
>  
> +static const struct attribute_group *hotplugable_cpu_attr_groups[] = {
> +#ifdef CONFIG_KEXEC
> +	&crash_note_cpu_attr_group,
> +#endif
> +#ifdef CONFIG_HOTPLUG_CPU
> +	&hotplug_cpu_attr_group,
> +#endif
> +	NULL
> +};
> +
>  /*
>   * Print cpu online, possible, present, and system maps
>   */
> @@ -265,9 +273,9 @@ int __cpuinit register_cpu(struct cpu *cpu, int num)
>  	cpu->dev.bus->uevent = arch_cpu_uevent;
>  #endif
>  	cpu->dev.groups = common_cpu_attr_groups;
> +	if (cpu->hotpluggable)
> +		cpu->dev.groups = hotplugable_cpu_attr_groups;
>  	error = device_register(&cpu->dev);
> -	if (!error && cpu->hotpluggable)
> -		register_cpu_control(cpu);
>  	if (!error)
>  		per_cpu(cpu_sys_devices, num) = &cpu->dev;
>  	if (!error)
> -- 
> 1.7.1
>