Re: [PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Silas Boyd-Wickizer]

On Fri, Aug 03, 2012 at 03:56:40PM +0200, Jean Delvare wrote:
> Hi Silas,
> 
> On Thu, 2 Aug 2012 17:07:08 -0700, Silas Boyd-Wickizer wrote:
> > via_cputemp_init in drivers/hwmon/via-cputemp.c loops with
> > for_each_online_cpu, adding platform_devices, then calls
> > register_hotcpu_notifier.  If a CPU is offlined between the loop and
> > register_hotcpu_notifier, then later onlined, via_cputemp_device_add
> > will attempt to platform devices with the same ID.
> 
> Missing word in this last sentence.

Fixed.

> 
> > 
> > This fix surrounds for_each_online_cpu and register_hotcpu_notifier
> > with get_online_cpus+put_online_cpus.
> > 
> > Build tested.
> 
> Thanks for reporting and for the fix. Two questions:
> 
> What about via_cputemp_exit()? While less obvious, I suspect it is racy
> too. The notifier is unregistered first. If a CPU gets offline before
> the devices are removed, we will have a device pointing to a
> non-existent CPU for a short time. I think we should play it safe and
> use get/put_online_cpus() there too, as I seem to understand it
> guarantees CPUs can't go offline when we wouldn't handle that event
> properly. Alternatively, unregistering the platform driver first might
> close the race.

I added get/put_online_cpus().

> 
> Secondly, drivers/hwmon/coretemp.c is very similar to via-cputemp.c, so
> I think it needs the exact same fix(es).

Indeed -- I'll submit a fix for this.

Silas

> 
> > 
> > Signed-off-by: Silas Boyd-Wickizer 
> > ---
> >  drivers/hwmon/via-cputemp.c |3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
> > index 8689664..9ad07c3 100644
> > --- a/drivers/hwmon/via-cputemp.c
> > +++ b/drivers/hwmon/via-cputemp.c
> > @@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
> > if (err)
> > goto exit;
> >  
> > +   get_online_cpus();
> > for_each_online_cpu(i) {
> > struct cpuinfo_x86 *c = _data(i);
> >  
> > @@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
> >  
> >  #ifndef CONFIG_HOTPLUG_CPU
> > if (list_empty(_list)) {
> > +   put_online_cpus();
> > err = -ENODEV;
> > goto exit_driver_unreg;
> > }
> >  #endif
> >  
> > register_hotcpu_notifier(_cputemp_cpu_notifier);
> > +   put_online_cpus();
> > return 0;
> >  
> >  #ifndef CONFIG_HOTPLUG_CPU
> 
> 
> -- 
> Jean Delvare
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Re: [PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Jean Delvare]

Hi Silas,

On Thu, 2 Aug 2012 17:07:08 -0700, Silas Boyd-Wickizer wrote:
> via_cputemp_init in drivers/hwmon/via-cputemp.c loops with
> for_each_online_cpu, adding platform_devices, then calls
> register_hotcpu_notifier.  If a CPU is offlined between the loop and
> register_hotcpu_notifier, then later onlined, via_cputemp_device_add
> will attempt to platform devices with the same ID.

Missing word in this last sentence.

> 
> This fix surrounds for_each_online_cpu and register_hotcpu_notifier
> with get_online_cpus+put_online_cpus.
> 
> Build tested.

Thanks for reporting and for the fix. Two questions:

What about via_cputemp_exit()? While less obvious, I suspect it is racy
too. The notifier is unregistered first. If a CPU gets offline before
the devices are removed, we will have a device pointing to a
non-existent CPU for a short time. I think we should play it safe and
use get/put_online_cpus() there too, as I seem to understand it
guarantees CPUs can't go offline when we wouldn't handle that event
properly. Alternatively, unregistering the platform driver first might
close the race.

Secondly, drivers/hwmon/coretemp.c is very similar to via-cputemp.c, so
I think it needs the exact same fix(es).

> 
> Signed-off-by: Silas Boyd-Wickizer 
> ---
>  drivers/hwmon/via-cputemp.c |3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
> index 8689664..9ad07c3 100644
> --- a/drivers/hwmon/via-cputemp.c
> +++ b/drivers/hwmon/via-cputemp.c
> @@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
>   if (err)
>   goto exit;
>  
> + get_online_cpus();
>   for_each_online_cpu(i) {
>   struct cpuinfo_x86 *c = _data(i);
>  
> @@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
>  
>  #ifndef CONFIG_HOTPLUG_CPU
>   if (list_empty(_list)) {
> + put_online_cpus();
>   err = -ENODEV;
>   goto exit_driver_unreg;
>   }
>  #endif
>  
>   register_hotcpu_notifier(_cputemp_cpu_notifier);
> + put_online_cpus();
>   return 0;
>  
>  #ifndef CONFIG_HOTPLUG_CPU


-- 
Jean Delvare
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Re: [PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Harald Welte]

Hi Silas,

thanks a lot for the finding and addressing the issue.

On Thu, Aug 02, 2012 at 05:07:08PM -0700, Silas Boyd-Wickizer wrote:
> Signed-off-by: Silas Boyd-Wickizer 

Acked-by: Harald Welte 

-- 
- Harald Weltehttp://laforge.gnumonks.org/

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  (ETSI EN 300 175-7 Ch. A6)
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Re: [PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Harald Welte]

Hi Silas,

thanks a lot for the finding and addressing the issue.

On Thu, Aug 02, 2012 at 05:07:08PM -0700, Silas Boyd-Wickizer wrote:
 Signed-off-by: Silas Boyd-Wickizer s...@mit.edu

Acked-by: Harald Welte lafo...@gnumonks.org

-- 
- Harald Welte lafo...@gnumonks.org   http://laforge.gnumonks.org/

Privacy in residential applications is a desirable marketing option.
  (ETSI EN 300 175-7 Ch. A6)
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Re: [PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Jean Delvare]

Hi Silas,

On Thu, 2 Aug 2012 17:07:08 -0700, Silas Boyd-Wickizer wrote:
 via_cputemp_init in drivers/hwmon/via-cputemp.c loops with
 for_each_online_cpu, adding platform_devices, then calls
 register_hotcpu_notifier.  If a CPU is offlined between the loop and
 register_hotcpu_notifier, then later onlined, via_cputemp_device_add
 will attempt to platform devices with the same ID.

Missing word in this last sentence.

 
 This fix surrounds for_each_online_cpu and register_hotcpu_notifier
 with get_online_cpus+put_online_cpus.
 
 Build tested.

Thanks for reporting and for the fix. Two questions:

What about via_cputemp_exit()? While less obvious, I suspect it is racy
too. The notifier is unregistered first. If a CPU gets offline before
the devices are removed, we will have a device pointing to a
non-existent CPU for a short time. I think we should play it safe and
use get/put_online_cpus() there too, as I seem to understand it
guarantees CPUs can't go offline when we wouldn't handle that event
properly. Alternatively, unregistering the platform driver first might
close the race.

Secondly, drivers/hwmon/coretemp.c is very similar to via-cputemp.c, so
I think it needs the exact same fix(es).

 
 Signed-off-by: Silas Boyd-Wickizer s...@mit.edu
 ---
  drivers/hwmon/via-cputemp.c |3 +++
  1 file changed, 3 insertions(+)
 
 diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
 index 8689664..9ad07c3 100644
 --- a/drivers/hwmon/via-cputemp.c
 +++ b/drivers/hwmon/via-cputemp.c
 @@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
   if (err)
   goto exit;
  
 + get_online_cpus();
   for_each_online_cpu(i) {
   struct cpuinfo_x86 *c = cpu_data(i);
  
 @@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
  
  #ifndef CONFIG_HOTPLUG_CPU
   if (list_empty(pdev_list)) {
 + put_online_cpus();
   err = -ENODEV;
   goto exit_driver_unreg;
   }
  #endif
  
   register_hotcpu_notifier(via_cputemp_cpu_notifier);
 + put_online_cpus();
   return 0;
  
  #ifndef CONFIG_HOTPLUG_CPU


-- 
Jean Delvare
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Re: [PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Silas Boyd-Wickizer]

On Fri, Aug 03, 2012 at 03:56:40PM +0200, Jean Delvare wrote:
 Hi Silas,
 
 On Thu, 2 Aug 2012 17:07:08 -0700, Silas Boyd-Wickizer wrote:
  via_cputemp_init in drivers/hwmon/via-cputemp.c loops with
  for_each_online_cpu, adding platform_devices, then calls
  register_hotcpu_notifier.  If a CPU is offlined between the loop and
  register_hotcpu_notifier, then later onlined, via_cputemp_device_add
  will attempt to platform devices with the same ID.
 
 Missing word in this last sentence.

Fixed.

 
  
  This fix surrounds for_each_online_cpu and register_hotcpu_notifier
  with get_online_cpus+put_online_cpus.
  
  Build tested.
 
 Thanks for reporting and for the fix. Two questions:
 
 What about via_cputemp_exit()? While less obvious, I suspect it is racy
 too. The notifier is unregistered first. If a CPU gets offline before
 the devices are removed, we will have a device pointing to a
 non-existent CPU for a short time. I think we should play it safe and
 use get/put_online_cpus() there too, as I seem to understand it
 guarantees CPUs can't go offline when we wouldn't handle that event
 properly. Alternatively, unregistering the platform driver first might
 close the race.

I added get/put_online_cpus().

 
 Secondly, drivers/hwmon/coretemp.c is very similar to via-cputemp.c, so
 I think it needs the exact same fix(es).

Indeed -- I'll submit a fix for this.

Silas

 
  
  Signed-off-by: Silas Boyd-Wickizer s...@mit.edu
  ---
   drivers/hwmon/via-cputemp.c |3 +++
   1 file changed, 3 insertions(+)
  
  diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
  index 8689664..9ad07c3 100644
  --- a/drivers/hwmon/via-cputemp.c
  +++ b/drivers/hwmon/via-cputemp.c
  @@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
  if (err)
  goto exit;
   
  +   get_online_cpus();
  for_each_online_cpu(i) {
  struct cpuinfo_x86 *c = cpu_data(i);
   
  @@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
   
   #ifndef CONFIG_HOTPLUG_CPU
  if (list_empty(pdev_list)) {
  +   put_online_cpus();
  err = -ENODEV;
  goto exit_driver_unreg;
  }
   #endif
   
  register_hotcpu_notifier(via_cputemp_cpu_notifier);
  +   put_online_cpus();
  return 0;
   
   #ifndef CONFIG_HOTPLUG_CPU
 
 
 -- 
 Jean Delvare
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[PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Silas Boyd-Wickizer]

via_cputemp_init in drivers/hwmon/via-cputemp.c loops with
for_each_online_cpu, adding platform_devices, then calls
register_hotcpu_notifier.  If a CPU is offlined between the loop and
register_hotcpu_notifier, then later onlined, via_cputemp_device_add
will attempt to platform devices with the same ID.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier
with get_online_cpus+put_online_cpus.

Build tested.

Signed-off-by: Silas Boyd-Wickizer 
---
 drivers/hwmon/via-cputemp.c |3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
index 8689664..9ad07c3 100644
--- a/drivers/hwmon/via-cputemp.c
+++ b/drivers/hwmon/via-cputemp.c
@@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
if (err)
goto exit;
 
+   get_online_cpus();
for_each_online_cpu(i) {
struct cpuinfo_x86 *c = _data(i);
 
@@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
 
 #ifndef CONFIG_HOTPLUG_CPU
if (list_empty(_list)) {
+   put_online_cpus();
err = -ENODEV;
goto exit_driver_unreg;
}
 #endif
 
register_hotcpu_notifier(_cputemp_cpu_notifier);
+   put_online_cpus();
return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU
-- 
1.7.10.4

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[PATCH 3/3] Use get_online_cpus to avoid races involving for_each_online_cpu

[Silas Boyd-Wickizer]

via_cputemp_init in drivers/hwmon/via-cputemp.c loops with
for_each_online_cpu, adding platform_devices, then calls
register_hotcpu_notifier.  If a CPU is offlined between the loop and
register_hotcpu_notifier, then later onlined, via_cputemp_device_add
will attempt to platform devices with the same ID.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier
with get_online_cpus+put_online_cpus.

Build tested.

Signed-off-by: Silas Boyd-Wickizer s...@mit.edu
---
 drivers/hwmon/via-cputemp.c |3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hwmon/via-cputemp.c b/drivers/hwmon/via-cputemp.c
index 8689664..9ad07c3 100644
--- a/drivers/hwmon/via-cputemp.c
+++ b/drivers/hwmon/via-cputemp.c
@@ -328,6 +328,7 @@ static int __init via_cputemp_init(void)
if (err)
goto exit;
 
+   get_online_cpus();
for_each_online_cpu(i) {
struct cpuinfo_x86 *c = cpu_data(i);
 
@@ -347,12 +348,14 @@ static int __init via_cputemp_init(void)
 
 #ifndef CONFIG_HOTPLUG_CPU
if (list_empty(pdev_list)) {
+   put_online_cpus();
err = -ENODEV;
goto exit_driver_unreg;
}
 #endif
 
register_hotcpu_notifier(via_cputemp_cpu_notifier);
+   put_online_cpus();
return 0;
 
 #ifndef CONFIG_HOTPLUG_CPU
-- 
1.7.10.4

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