Re: [PATCH] net: fix a data race when get vlan device

Re: [PATCH] net: fix a data race when get vlan device

[zhudi (J)]

> dependencyOn 2021/4/15 11:35, zhudi wrote:
> > From: Di Zhu <zhudi21@huawei.com>
> >
> > We encountered a crash: in the packet receiving process, we got an
> > illegal VLAN device address, but the VLAN device address saved in
> > vmcore is correct. After checking the code, we found a possible data
> > competition:
> > CPU 0:                             CPU 1:
> >     (RCU read lock)                  (RTNL lock)
> >     vlan_do_receive()		       register_vlan_dev()
> >       vlan_find_dev()
> >
> >         ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()
> >
> > In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
> > executed before assigning a value to vlan devices array, otherwise we
> 
> As my understanding, there is a dependency between calling kzalloc() and
> assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays,
> CPU and compiler can see the dependency, why can't it handling the
> dependency before adding the smp_wmb()?
> 
> See CONTROL DEPENDENCIES section in Documentation/memory-
> barriers.txt:
> 
> However, stores are not speculated.  This means that ordering -is- provided
> for load-store control dependencies, as in the following example:
> 
>         q = READ_ONCE(a);
>         if (q) {
>                 WRITE_ONCE(b, 1);
>         }
> 

 Maybe I didn't make it clear.  This memory isolation is to ensure the order of
 memset(object, 0, size) in kzalloc() operations and the subsequent array assignment statements.

kzalloc()
    ->memset(object, 0, size)

smp_wmb()

vg->vlan_devices_arrays[pidx][vidx] = array;

Because __vlan_group_get_device() function depends on this order

> 
> 
> > may get a wrong address from the hardware cache on another cpu.
> >
> > So fix it by adding memory barrier instruction to ensure the order of
> > memory operations.
> >
> > Signed-off-by: Di Zhu <zhudi21@huawei.com>
> > ---
> >  net/8021q/vlan.c | 2 ++
> >  net/8021q/vlan.h | 3 +++
> >  2 files changed, 5 insertions(+)
> >
> > diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index
> > 8b644113715e..4f541e05cd3f 100644
> > --- a/net/8021q/vlan.c
> > +++ b/net/8021q/vlan.c
> > @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group
> *vg,
> >  	if (array == NULL)
> >  		return -ENOBUFS;
> >
> > +	smp_wmb();
> > +
> >  	vg->vlan_devices_arrays[pidx][vidx] = array;
> >  	return 0;
> >  }
> > diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h index
> > 953405362795..7408fda084d3 100644
> > --- a/net/8021q/vlan.h
> > +++ b/net/8021q/vlan.h
> > @@ -57,6 +57,9 @@ static inline struct net_device
> > *__vlan_group_get_device(struct vlan_group *vg,
> >
> >  	array = vg->vlan_devices_arrays[pidx]
> >  				       [vlan_id /
> VLAN_GROUP_ARRAY_PART_LEN];
> > +
> > +	smp_rmb();
> > +
> >  	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] :
> NULL;  }
> >
> >

Re: [PATCH] net: fix a data race when get vlan device

[Yunsheng Lin]

On 2021/4/16 11:27, zhudi (J) wrote:
>> dependencyOn 2021/4/15 11:35, zhudi wrote:
>>> From: Di Zhu <zhudi21@huawei.com>
>>>
>>> We encountered a crash: in the packet receiving process, we got an
>>> illegal VLAN device address, but the VLAN device address saved in
>>> vmcore is correct. After checking the code, we found a possible data
>>> competition:
>>> CPU 0:                             CPU 1:
>>>     (RCU read lock)                  (RTNL lock)
>>>     vlan_do_receive()		       register_vlan_dev()
>>>       vlan_find_dev()
>>>
>>>         ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()
>>>
>>> In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
>>> executed before assigning a value to vlan devices array, otherwise we
>>
>> As my understanding, there is a dependency between calling kzalloc() and
>> assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays,
>> CPU and compiler can see the dependency, why can't it handling the
>> dependency before adding the smp_wmb()?
>>
>> See CONTROL DEPENDENCIES section in Documentation/memory-
>> barriers.txt:
>>
>> However, stores are not speculated.  This means that ordering -is- provided
>> for load-store control dependencies, as in the following example:
>>
>>         q = READ_ONCE(a);
>>         if (q) {
>>                 WRITE_ONCE(b, 1);
>>         }
>>
> 
>  Maybe I didn't make it clear.  This memory isolation is to ensure the order of
>  memset(object, 0, size) in kzalloc() operations and the subsequent array assignment statements.
> 
> kzalloc()
>     ->memset(object, 0, size)
> 
> smp_wmb()
> 
> vg->vlan_devices_arrays[pidx][vidx] = array;
> 
> Because __vlan_group_get_device() function depends on this order

Thanks for clarify, it would be good to mention this in the
commit log too.

Also, __vlan_group_get_device() is used in the data path, it would
be to avoid the barrier op too. Maybe using rcu to avoid the barrier
if the __vlan_group_get_device() is already protected by rcu_lock.


> 
>>
>>
>>> may get a wrong address from the hardware cache on another cpu.
>>>
>>> So fix it by adding memory barrier instruction to ensure the order of
>>> memory operations.
>>>
>>> Signed-off-by: Di Zhu <zhudi21@huawei.com>
>>> ---
>>>  net/8021q/vlan.c | 2 ++
>>>  net/8021q/vlan.h | 3 +++
>>>  2 files changed, 5 insertions(+)
>>>
>>> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index
>>> 8b644113715e..4f541e05cd3f 100644
>>> --- a/net/8021q/vlan.c
>>> +++ b/net/8021q/vlan.c
>>> @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group
>> *vg,
>>>  	if (array == NULL)
>>>  		return -ENOBUFS;
>>>
>>> +	smp_wmb();
>>> +
>>>  	vg->vlan_devices_arrays[pidx][vidx] = array;
>>>  	return 0;
>>>  }
>>> diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h index
>>> 953405362795..7408fda084d3 100644
>>> --- a/net/8021q/vlan.h
>>> +++ b/net/8021q/vlan.h
>>> @@ -57,6 +57,9 @@ static inline struct net_device
>>> *__vlan_group_get_device(struct vlan_group *vg,
>>>
>>>  	array = vg->vlan_devices_arrays[pidx]
>>>  				       [vlan_id /
>> VLAN_GROUP_ARRAY_PART_LEN];
>>> +
>>> +	smp_rmb();
>>> +
>>>  	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] :
>> NULL;  }
>>>
>>>
> 

Re: [PATCH] net: fix a data race when get vlan device

[zhudi (J)]

> On 2021/4/17 20:33, zhudi (J) wrote:
> >> On 2021/4/16 11:27, zhudi (J) wrote:
> >>>> dependencyOn 2021/4/15 11:35, zhudi wrote:
> >>>>> From: Di Zhu <zhudi21@huawei.com>
> >>>>>
> >>>>> We encountered a crash: in the packet receiving process, we got an
> >>>>> illegal VLAN device address, but the VLAN device address saved in
> >>>>> vmcore is correct. After checking the code, we found a possible
> >>>>> data
> >>>>> competition:
> >>>>> CPU 0:                             CPU 1:
> >>>>>     (RCU read lock)                  (RTNL lock)
> >>>>>     vlan_do_receive()		       register_vlan_dev()
> >>>>>       vlan_find_dev()
> >>>>>
> >>>>>         ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()
> >>>>>
> >>>>> In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
> >>>>> executed before assigning a value to vlan devices array, otherwise
> >>>>> we
> >>>>
> >>>> As my understanding, there is a dependency between calling
> >>>> kzalloc() and assigning the address(returned from kzalloc()) to
> >>>> vg->vlan_devices_arrays, CPU and compiler can see the dependency,
> >>>> why can't it handling the dependency before adding the smp_wmb()?
> >>>>
> >>>> See CONTROL DEPENDENCIES section in Documentation/memory-
> >>>> barriers.txt:
> >>>>
> >>>> However, stores are not speculated.  This means that ordering -is-
> >> provided
> >>>> for load-store control dependencies, as in the following example:
> >>>>
> >>>>         q = READ_ONCE(a);
> >>>>         if (q) {
> >>>>                 WRITE_ONCE(b, 1);
> >>>>         }
> >>>>
> >>>
> >>>  Maybe I didn't make it clear.  This memory isolation is to ensure
> >>> the order
> >> of
> >>>  memset(object, 0, size) in kzalloc() operations and the subsequent
> >>> array
> >> assignment statements.
> >>>
> >>> kzalloc()
> >>>     ->memset(object, 0, size)
> >>>
> >>> smp_wmb()
> >>>
> >>> vg->vlan_devices_arrays[pidx][vidx] = array;
> >>>
> >>> Because __vlan_group_get_device() function depends on this order
> >>
> >
> >> Thanks for clarify, it would be good to mention this in the commit
> >> log too.
> >
> > OK,  I'll change it.  Thank you for your advice.
> >
> >>
> >> Also, __vlan_group_get_device() is used in the data path, it would be
> >> to avoid the barrier op too. Maybe using rcu to avoid the barrier if
> >> the __vlan_group_get_device() is already protected by rcu_lock.
> >
> > Using the netperf command for testing on x86, there is no difference in
> performance:
> 
> This may make sense for x86 because x86 has a strong order memory model,
> which has smp_rmb() as compiler barrier, as my understanding.
> 
> How about the weak order memory model CPU? such as arm64, which has
> smp_rmb() as 'dmb' instruction.

The test result on Arm is the same as that on X86, no matter whether it is patched or not,
there is basically no difference in performance.

The smp_rmb() semantically does not ensure the completion of any of the
memory accesses for which it ensures relative order, So the performance impact
should be minimal

> Also the cpu usage may need to be looked at if data rate is at line speed.
> 
> >
> > # netperf -H 112.113.0.12 -l 20 -t TCP_STREAM MIGRATED TCP STREAM
> TEST
> > from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 112.113.0.12 () port 0 AF_INET
> > Recv   Send    Send
> > Socket Socket  Message  Elapsed
> > Size   Size    Size     Time     Throughput
> > bytes  bytes   bytes    secs.    10^6bits/sec
> >
> > 131072  16384  16384    20.00    9386.03
> >
> > After patch:
> >
> >  # netperf -H 112.113.0.12 -l 20 -t TCP_STREAM MIGRATED TCP STREAM
> > TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 112.113.0.12 () port 0 AF_INET
> > Recv   Send    Send
> > Socket Socket  Message  Elapsed
> > Size   Size    Size     Time     Throughput
> > bytes  bytes   bytes    secs.    10^6bits/sec
> >
> > 131072  16384  16384    20.00    9386.41
> >
> > The same is true for UDP stream test
> >
> >>
> >>>
> >>>>
> >>>>
> >>>>> may get a wrong address from the hardware cache on another cpu.
> >>>>>
> >>>>> So fix it by adding memory barrier instruction to ensure the order
> >>>>> of memory operations.
> >>>>>
> >>>>> Signed-off-by: Di Zhu <zhudi21@huawei.com>
> >>>>> ---
> >>>>>  net/8021q/vlan.c | 2 ++
> >>>>>  net/8021q/vlan.h | 3 +++
> >>>>>  2 files changed, 5 insertions(+)
> >>>>>
> >>>>> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index
> >>>>> 8b644113715e..4f541e05cd3f 100644
> >>>>> --- a/net/8021q/vlan.c
> >>>>> +++ b/net/8021q/vlan.c
> >>>>> @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct
> >> vlan_group
> >>>> *vg,
> >>>>>  	if (array == NULL)
> >>>>>  		return -ENOBUFS;
> >>>>>
> >>>>> +	smp_wmb();
> >>>>> +
> >>>>>  	vg->vlan_devices_arrays[pidx][vidx] = array;
> >>>>>  	return 0;
> >>>>>  }
> >>>>> diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h index
> >>>>> 953405362795..7408fda084d3 100644
> >>>>> --- a/net/8021q/vlan.h
> >>>>> +++ b/net/8021q/vlan.h
> >>>>> @@ -57,6 +57,9 @@ static inline struct net_device
> >>>>> *__vlan_group_get_device(struct vlan_group *vg,
> >>>>>
> >>>>>  	array = vg->vlan_devices_arrays[pidx]
> >>>>>  				       [vlan_id /
> >>>> VLAN_GROUP_ARRAY_PART_LEN];
> >>>>> +
> >>>>> +	smp_rmb();
> >>>>> +
> >>>>>  	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] :
> >>>> NULL;  }
> >>>>>
> >>>>>
> >>>
> >

Re: [PATCH] net: fix a data race when get vlan device

[Yunsheng Lin]

On 2021/4/17 20:33, zhudi (J) wrote:
>> On 2021/4/16 11:27, zhudi (J) wrote:
>>>> dependencyOn 2021/4/15 11:35, zhudi wrote:
>>>>> From: Di Zhu <zhudi21@huawei.com>
>>>>>
>>>>> We encountered a crash: in the packet receiving process, we got an
>>>>> illegal VLAN device address, but the VLAN device address saved in
>>>>> vmcore is correct. After checking the code, we found a possible data
>>>>> competition:
>>>>> CPU 0:                             CPU 1:
>>>>>     (RCU read lock)                  (RTNL lock)
>>>>>     vlan_do_receive()		       register_vlan_dev()
>>>>>       vlan_find_dev()
>>>>>
>>>>>         ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()
>>>>>
>>>>> In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
>>>>> executed before assigning a value to vlan devices array, otherwise we
>>>>
>>>> As my understanding, there is a dependency between calling kzalloc() and
>>>> assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays,
>>>> CPU and compiler can see the dependency, why can't it handling the
>>>> dependency before adding the smp_wmb()?
>>>>
>>>> See CONTROL DEPENDENCIES section in Documentation/memory-
>>>> barriers.txt:
>>>>
>>>> However, stores are not speculated.  This means that ordering -is-
>> provided
>>>> for load-store control dependencies, as in the following example:
>>>>
>>>>         q = READ_ONCE(a);
>>>>         if (q) {
>>>>                 WRITE_ONCE(b, 1);
>>>>         }
>>>>
>>>
>>>  Maybe I didn't make it clear.  This memory isolation is to ensure the order
>> of
>>>  memset(object, 0, size) in kzalloc() operations and the subsequent array
>> assignment statements.
>>>
>>> kzalloc()
>>>     ->memset(object, 0, size)
>>>
>>> smp_wmb()
>>>
>>> vg->vlan_devices_arrays[pidx][vidx] = array;
>>>
>>> Because __vlan_group_get_device() function depends on this order
>>
> 
>> Thanks for clarify, it would be good to mention this in the
>> commit log too.
> 
> OK,  I'll change it.  Thank you for your advice.
> 
>>
>> Also, __vlan_group_get_device() is used in the data path, it would
>> be to avoid the barrier op too. Maybe using rcu to avoid the barrier
>> if the __vlan_group_get_device() is already protected by rcu_lock.
> 
> Using the netperf command for testing on x86, there is no difference in performance:

This may make sense for x86 because x86 has a strong order memory
model, which has smp_rmb() as compiler barrier, as my understanding.

How about the weak order memory model CPU? such as arm64, which has
smp_rmb() as 'dmb' instruction.

Also the cpu usage may need to be looked at if data rate is
at line speed.

> 
> # netperf -H 112.113.0.12 -l 20 -t TCP_STREAM
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 112.113.0.12 () port 0 AF_INET
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
> 131072  16384  16384    20.00    9386.03
> 
> After patch:
> 
>  # netperf -H 112.113.0.12 -l 20 -t TCP_STREAM
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 112.113.0.12 () port 0 AF_INET
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
> 131072  16384  16384    20.00    9386.41
> 
> The same is true for UDP stream test
> 
>>
>>>
>>>>
>>>>
>>>>> may get a wrong address from the hardware cache on another cpu.
>>>>>
>>>>> So fix it by adding memory barrier instruction to ensure the order of
>>>>> memory operations.
>>>>>
>>>>> Signed-off-by: Di Zhu <zhudi21@huawei.com>
>>>>> ---
>>>>>  net/8021q/vlan.c | 2 ++
>>>>>  net/8021q/vlan.h | 3 +++
>>>>>  2 files changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index
>>>>> 8b644113715e..4f541e05cd3f 100644
>>>>> --- a/net/8021q/vlan.c
>>>>> +++ b/net/8021q/vlan.c
>>>>> @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct
>> vlan_group
>>>> *vg,
>>>>>  	if (array == NULL)
>>>>>  		return -ENOBUFS;
>>>>>
>>>>> +	smp_wmb();
>>>>> +
>>>>>  	vg->vlan_devices_arrays[pidx][vidx] = array;
>>>>>  	return 0;
>>>>>  }
>>>>> diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h index
>>>>> 953405362795..7408fda084d3 100644
>>>>> --- a/net/8021q/vlan.h
>>>>> +++ b/net/8021q/vlan.h
>>>>> @@ -57,6 +57,9 @@ static inline struct net_device
>>>>> *__vlan_group_get_device(struct vlan_group *vg,
>>>>>
>>>>>  	array = vg->vlan_devices_arrays[pidx]
>>>>>  				       [vlan_id /
>>>> VLAN_GROUP_ARRAY_PART_LEN];
>>>>> +
>>>>> +	smp_rmb();
>>>>> +
>>>>>  	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] :
>>>> NULL;  }
>>>>>
>>>>>
>>>
> 

Re: [PATCH] net: fix a data race when get vlan device

[zhudi (J)]

> On 2021/4/16 11:27, zhudi (J) wrote:
> >> dependencyOn 2021/4/15 11:35, zhudi wrote:
> >>> From: Di Zhu <zhudi21@huawei.com>
> >>>
> >>> We encountered a crash: in the packet receiving process, we got an
> >>> illegal VLAN device address, but the VLAN device address saved in
> >>> vmcore is correct. After checking the code, we found a possible data
> >>> competition:
> >>> CPU 0:                             CPU 1:
> >>>     (RCU read lock)                  (RTNL lock)
> >>>     vlan_do_receive()		       register_vlan_dev()
> >>>       vlan_find_dev()
> >>>
> >>>         ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()
> >>>
> >>> In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
> >>> executed before assigning a value to vlan devices array, otherwise we
> >>
> >> As my understanding, there is a dependency between calling kzalloc() and
> >> assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays,
> >> CPU and compiler can see the dependency, why can't it handling the
> >> dependency before adding the smp_wmb()?
> >>
> >> See CONTROL DEPENDENCIES section in Documentation/memory-
> >> barriers.txt:
> >>
> >> However, stores are not speculated.  This means that ordering -is-
> provided
> >> for load-store control dependencies, as in the following example:
> >>
> >>         q = READ_ONCE(a);
> >>         if (q) {
> >>                 WRITE_ONCE(b, 1);
> >>         }
> >>
> >
> >  Maybe I didn't make it clear.  This memory isolation is to ensure the order
> of
> >  memset(object, 0, size) in kzalloc() operations and the subsequent array
> assignment statements.
> >
> > kzalloc()
> >     ->memset(object, 0, size)
> >
> > smp_wmb()
> >
> > vg->vlan_devices_arrays[pidx][vidx] = array;
> >
> > Because __vlan_group_get_device() function depends on this order
> 

> Thanks for clarify, it would be good to mention this in the
> commit log too.

OK,  I'll change it.  Thank you for your advice.

> 
> Also, __vlan_group_get_device() is used in the data path, it would
> be to avoid the barrier op too. Maybe using rcu to avoid the barrier
> if the __vlan_group_get_device() is already protected by rcu_lock.

Using the netperf command for testing on x86, there is no difference in performance:

# netperf -H 112.113.0.12 -l 20 -t TCP_STREAM
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 112.113.0.12 () port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

131072  16384  16384    20.00    9386.03

After patch:

 # netperf -H 112.113.0.12 -l 20 -t TCP_STREAM
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 112.113.0.12 () port 0 AF_INET
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

131072  16384  16384    20.00    9386.41

The same is true for UDP stream test

> 
> >
> >>
> >>
> >>> may get a wrong address from the hardware cache on another cpu.
> >>>
> >>> So fix it by adding memory barrier instruction to ensure the order of
> >>> memory operations.
> >>>
> >>> Signed-off-by: Di Zhu <zhudi21@huawei.com>
> >>> ---
> >>>  net/8021q/vlan.c | 2 ++
> >>>  net/8021q/vlan.h | 3 +++
> >>>  2 files changed, 5 insertions(+)
> >>>
> >>> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c index
> >>> 8b644113715e..4f541e05cd3f 100644
> >>> --- a/net/8021q/vlan.c
> >>> +++ b/net/8021q/vlan.c
> >>> @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct
> vlan_group
> >> *vg,
> >>>  	if (array == NULL)
> >>>  		return -ENOBUFS;
> >>>
> >>> +	smp_wmb();
> >>> +
> >>>  	vg->vlan_devices_arrays[pidx][vidx] = array;
> >>>  	return 0;
> >>>  }
> >>> diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h index
> >>> 953405362795..7408fda084d3 100644
> >>> --- a/net/8021q/vlan.h
> >>> +++ b/net/8021q/vlan.h
> >>> @@ -57,6 +57,9 @@ static inline struct net_device
> >>> *__vlan_group_get_device(struct vlan_group *vg,
> >>>
> >>>  	array = vg->vlan_devices_arrays[pidx]
> >>>  				       [vlan_id /
> >> VLAN_GROUP_ARRAY_PART_LEN];
> >>> +
> >>> +	smp_rmb();
> >>> +
> >>>  	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] :
> >> NULL;  }
> >>>
> >>>
> >

Re: [PATCH] net: fix a data race when get vlan device

[Yunsheng Lin]

dependencyOn 2021/4/15 11:35, zhudi wrote:
> From: Di Zhu <zhudi21@huawei.com>
> 
> We encountered a crash: in the packet receiving process, we got an
> illegal VLAN device address, but the VLAN device address saved in vmcore
> is correct. After checking the code, we found a possible data
> competition:
> CPU 0:                             CPU 1:
>     (RCU read lock)                  (RTNL lock)
>     vlan_do_receive()		       register_vlan_dev()
>       vlan_find_dev()
> 
>         ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()
> 
> In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
> executed before assigning a value to vlan devices array, otherwise we

As my understanding, there is a dependency between calling kzalloc() and
assigning the address(returned from kzalloc()) to vg->vlan_devices_arrays,
CPU and compiler can see the dependency, why can't it handling the
dependency before adding the smp_wmb()?

See CONTROL DEPENDENCIES section in Documentation/memory-barriers.txt:

However, stores are not speculated.  This means that ordering -is- provided
for load-store control dependencies, as in the following example:

        q = READ_ONCE(a);
        if (q) {
                WRITE_ONCE(b, 1);
        }



> may get a wrong address from the hardware cache on another cpu.
> 
> So fix it by adding memory barrier instruction to ensure the order
> of memory operations.
> 
> Signed-off-by: Di Zhu <zhudi21@huawei.com>
> ---
>  net/8021q/vlan.c | 2 ++
>  net/8021q/vlan.h | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
> index 8b644113715e..4f541e05cd3f 100644
> --- a/net/8021q/vlan.c
> +++ b/net/8021q/vlan.c
> @@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group *vg,
>  	if (array == NULL)
>  		return -ENOBUFS;
>  
> +	smp_wmb();
> +
>  	vg->vlan_devices_arrays[pidx][vidx] = array;
>  	return 0;
>  }
> diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h
> index 953405362795..7408fda084d3 100644
> --- a/net/8021q/vlan.h
> +++ b/net/8021q/vlan.h
> @@ -57,6 +57,9 @@ static inline struct net_device *__vlan_group_get_device(struct vlan_group *vg,
>  
>  	array = vg->vlan_devices_arrays[pidx]
>  				       [vlan_id / VLAN_GROUP_ARRAY_PART_LEN];
> +
> +	smp_rmb();
> +
>  	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL;
>  }
>  
> 

[PATCH] net: fix a data race when get vlan device

[zhudi]

From: Di Zhu <zhudi21@huawei.com>

We encountered a crash: in the packet receiving process, we got an
illegal VLAN device address, but the VLAN device address saved in vmcore
is correct. After checking the code, we found a possible data
competition:
CPU 0:                             CPU 1:
    (RCU read lock)                  (RTNL lock)
    vlan_do_receive()		       register_vlan_dev()
      vlan_find_dev()

        ->__vlan_group_get_device()	 ->vlan_group_prealloc_vid()

In vlan_group_prealloc_vid(), We need to make sure that kzalloc is
executed before assigning a value to vlan devices array, otherwise we
may get a wrong address from the hardware cache on another cpu.

So fix it by adding memory barrier instruction to ensure the order
of memory operations.

Signed-off-by: Di Zhu <zhudi21@huawei.com>
---
 net/8021q/vlan.c | 2 ++
 net/8021q/vlan.h | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 8b644113715e..4f541e05cd3f 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -71,6 +71,8 @@ static int vlan_group_prealloc_vid(struct vlan_group *vg,
 	if (array == NULL)
 		return -ENOBUFS;
 
+	smp_wmb();
+
 	vg->vlan_devices_arrays[pidx][vidx] = array;
 	return 0;
 }
diff --git a/net/8021q/vlan.h b/net/8021q/vlan.h
index 953405362795..7408fda084d3 100644
--- a/net/8021q/vlan.h
+++ b/net/8021q/vlan.h
@@ -57,6 +57,9 @@ static inline struct net_device *__vlan_group_get_device(struct vlan_group *vg,
 
 	array = vg->vlan_devices_arrays[pidx]
 				       [vlan_id / VLAN_GROUP_ARRAY_PART_LEN];
+
+	smp_rmb();
+
 	return array ? array[vlan_id % VLAN_GROUP_ARRAY_PART_LEN] : NULL;
 }
 
-- 
2.23.0