[PATCH] ptr_ring: add barriers

[PATCH] ptr_ring: add barriers

[Michael S. Tsirkin]

Users of ptr_ring expect that it's safe to give the
data structure a pointer and have it be available
to consumers, but that actually requires an smb_wmb
or a stronger barrier.

In absence of such barriers and on architectures that reorder writes,
consumer might read an un=initialized value from an skb pointer stored
in the skb array.  This was observed causing crashes.

To fix, add memory barriers.  The barrier we use is a wmb, the
assumption being that producers do not need to read the value so we do
not need to order these reads.

Reported-by: George Cherian <george.cherian@cavium.com>
Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

George, could you pls report whether this patch fixes
the issue for you?

This seems to be needed in stable as well.




 include/linux/ptr_ring.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 37b4bb2..6866df4 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
 
 /* Note: callers invoking this in a loop must use a compiler barrier,
  * for example cpu_relax(). Callers must hold producer_lock.
+ * Callers are responsible for making sure pointer that is being queued
+ * points to a valid data.
  */
 static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
 {
 	if (unlikely(!r->size) || r->queue[r->producer])
 		return -ENOSPC;
 
+	/* Make sure the pointer we are storing points to a valid data. */
+	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
+	smp_wmb();
+
 	r->queue[r->producer++] = ptr;
 	if (unlikely(r->producer >= r->size))
 		r->producer = 0;
@@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
 	if (ptr)
 		__ptr_ring_discard_one(r);
 
+	/* Make sure anyone accessing data through the pointer is up to date. */
+	/* Pairs with smp_wmb in __ptr_ring_produce. */
+	smp_read_barrier_depends();
 	return ptr;
 }
 
-- 
MST

Re: [PATCH] ptr_ring: add barriers

[Jason Wang]

On 2017年12月06日 03:29, Michael S. Tsirkin wrote:
> Users of ptr_ring expect that it's safe to give the
> data structure a pointer and have it be available
> to consumers, but that actually requires an smb_wmb
> or a stronger barrier.
>
> In absence of such barriers and on architectures that reorder writes,
> consumer might read an un=initialized value from an skb pointer stored
> in the skb array.  This was observed causing crashes.
>
> To fix, add memory barriers.  The barrier we use is a wmb, the
> assumption being that producers do not need to read the value so we do
> not need to order these reads.
>
> Reported-by: George Cherian <george.cherian@cavium.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>
> George, could you pls report whether this patch fixes
> the issue for you?
>
> This seems to be needed in stable as well.
>
>
>
>
>   include/linux/ptr_ring.h | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 37b4bb2..6866df4 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
>   
>   /* Note: callers invoking this in a loop must use a compiler barrier,
>    * for example cpu_relax(). Callers must hold producer_lock.
> + * Callers are responsible for making sure pointer that is being queued
> + * points to a valid data.
>    */
>   static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
>   {
>   	if (unlikely(!r->size) || r->queue[r->producer])
>   		return -ENOSPC;
>   
> +	/* Make sure the pointer we are storing points to a valid data. */
> +	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
> +	smp_wmb();
> +
>   	r->queue[r->producer++] = ptr;
>   	if (unlikely(r->producer >= r->size))
>   		r->producer = 0;
> @@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
>   	if (ptr)
>   		__ptr_ring_discard_one(r);
>   
> +	/* Make sure anyone accessing data through the pointer is up to date. */
> +	/* Pairs with smp_wmb in __ptr_ring_produce. */
> +	smp_read_barrier_depends();
>   	return ptr;
>   }
>   

I was thinking whether or not it's better to move those to the callers. 
Then we can save lots of barriers in e.g batch consuming.

Thanks

Re: [PATCH] ptr_ring: add barriers

[Michael S. Tsirkin]

On Wed, Dec 06, 2017 at 10:31:39AM +0800, Jason Wang wrote:
> 
> 
> On 2017年12月06日 03:29, Michael S. Tsirkin wrote:
> > Users of ptr_ring expect that it's safe to give the
> > data structure a pointer and have it be available
> > to consumers, but that actually requires an smb_wmb
> > or a stronger barrier.
> > 
> > In absence of such barriers and on architectures that reorder writes,
> > consumer might read an un=initialized value from an skb pointer stored
> > in the skb array.  This was observed causing crashes.
> > 
> > To fix, add memory barriers.  The barrier we use is a wmb, the
> > assumption being that producers do not need to read the value so we do
> > not need to order these reads.
> > 
> > Reported-by: George Cherian <george.cherian@cavium.com>
> > Suggested-by: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > George, could you pls report whether this patch fixes
> > the issue for you?
> > 
> > This seems to be needed in stable as well.
> > 
> > 
> > 
> > 
> >   include/linux/ptr_ring.h | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> > 
> > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> > index 37b4bb2..6866df4 100644
> > --- a/include/linux/ptr_ring.h
> > +++ b/include/linux/ptr_ring.h
> > @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
> >   /* Note: callers invoking this in a loop must use a compiler barrier,
> >    * for example cpu_relax(). Callers must hold producer_lock.
> > + * Callers are responsible for making sure pointer that is being queued
> > + * points to a valid data.
> >    */
> >   static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
> >   {
> >   	if (unlikely(!r->size) || r->queue[r->producer])
> >   		return -ENOSPC;
> > +	/* Make sure the pointer we are storing points to a valid data. */
> > +	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
> > +	smp_wmb();
> > +
> >   	r->queue[r->producer++] = ptr;
> >   	if (unlikely(r->producer >= r->size))
> >   		r->producer = 0;
> > @@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
> >   	if (ptr)
> >   		__ptr_ring_discard_one(r);
> > +	/* Make sure anyone accessing data through the pointer is up to date. */
> > +	/* Pairs with smp_wmb in __ptr_ring_produce. */
> > +	smp_read_barrier_depends();
> >   	return ptr;
> >   }
> 
> I was thinking whether or not it's better to move those to the callers. Then
> we can save lots of barriers in e.g batch consuming.
> 
> Thanks

Batch consumers only do smp_read_barrier_depends which is free on
non-alpha. I suggest we do the simple thing for stable and reserve
optimizations for later.

-- 
MST

Re: [PATCH] ptr_ring: add barriers

[Jason Wang]

On 2017年12月06日 10:53, Michael S. Tsirkin wrote:
> On Wed, Dec 06, 2017 at 10:31:39AM +0800, Jason Wang wrote:
>>
>> On 2017年12月06日 03:29, Michael S. Tsirkin wrote:
>>> Users of ptr_ring expect that it's safe to give the
>>> data structure a pointer and have it be available
>>> to consumers, but that actually requires an smb_wmb
>>> or a stronger barrier.
>>>
>>> In absence of such barriers and on architectures that reorder writes,
>>> consumer might read an un=initialized value from an skb pointer stored
>>> in the skb array.  This was observed causing crashes.
>>>
>>> To fix, add memory barriers.  The barrier we use is a wmb, the
>>> assumption being that producers do not need to read the value so we do
>>> not need to order these reads.
>>>
>>> Reported-by: George Cherian <george.cherian@cavium.com>
>>> Suggested-by: Jason Wang <jasowang@redhat.com>
>>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>>> ---
>>>
>>> George, could you pls report whether this patch fixes
>>> the issue for you?
>>>
>>> This seems to be needed in stable as well.
>>>
>>>
>>>
>>>
>>>    include/linux/ptr_ring.h | 9 +++++++++
>>>    1 file changed, 9 insertions(+)
>>>
>>> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
>>> index 37b4bb2..6866df4 100644
>>> --- a/include/linux/ptr_ring.h
>>> +++ b/include/linux/ptr_ring.h
>>> @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
>>>    /* Note: callers invoking this in a loop must use a compiler barrier,
>>>     * for example cpu_relax(). Callers must hold producer_lock.
>>> + * Callers are responsible for making sure pointer that is being queued
>>> + * points to a valid data.
>>>     */
>>>    static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
>>>    {
>>>    	if (unlikely(!r->size) || r->queue[r->producer])
>>>    		return -ENOSPC;
>>> +	/* Make sure the pointer we are storing points to a valid data. */
>>> +	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
>>> +	smp_wmb();
>>> +
>>>    	r->queue[r->producer++] = ptr;
>>>    	if (unlikely(r->producer >= r->size))
>>>    		r->producer = 0;
>>> @@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
>>>    	if (ptr)
>>>    		__ptr_ring_discard_one(r);
>>> +	/* Make sure anyone accessing data through the pointer is up to date. */
>>> +	/* Pairs with smp_wmb in __ptr_ring_produce. */
>>> +	smp_read_barrier_depends();
>>>    	return ptr;
>>>    }
>> I was thinking whether or not it's better to move those to the callers. Then
>> we can save lots of barriers in e.g batch consuming.
>>
>> Thanks
> Batch consumers only do smp_read_barrier_depends which is free on
> non-alpha. I suggest we do the simple thing for stable and reserve
> optimizations for later.
>

Right.

Acked-by: Jason Wang <jasowang@redhat.com>

Re: [PATCH] ptr_ring: add barriers

[George Cherian]

Hi Michael,


On 12/06/2017 12:59 AM, Michael S. Tsirkin wrote:
> Users of ptr_ring expect that it's safe to give the
> data structure a pointer and have it be available
> to consumers, but that actually requires an smb_wmb
> or a stronger barrier.
This is not the exact situation we are seeing.
Let me try to explain the situation

Affected on ARM64 platform.
1) tun_net_xmit calls skb_array_produce, which pushes the skb to the 
ptr_ring, this push is protected by a producer_lock.

2)Prior to this call the tun_net_xmit calls skb_orphan which calls the 
skb->destructor and sets skb->destructor and skb->sk as NULL.

2.a) These 2 writes are getting reordered

3) At the same time in the receive side (tun_ring_recv), which gets 
executed in another core calls skb_array_consume which pulls the skb 
from  ptr ring, this pull is protected by a consumer lock.

4) eventually calling the skb->destructor (sock_wfree) with stale values.

Also note that this issue is reproducible in a long run and doesn't 
happen immediately after the launch of multiple VM's (infact the 
particular test cases launches 56 VM's which does iperf back and forth)

> 
> In absence of such barriers and on architectures that reorder writes,
> consumer might read an un=initialized value from an skb pointer stored
> in the skb array.  This was observed causing crashes.
> 
> To fix, add memory barriers.  The barrier we use is a wmb, the
> assumption being that producers do not need to read the value so we do
> not need to order these reads.
It is not the case that producer is reading the value, but the consumer 
reading stale value. So we need to have a strict rmb in place .

> 
> Reported-by: George Cherian <george.cherian@cavium.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> George, could you pls report whether this patch fixes
> the issue for you?
> 
> This seems to be needed in stable as well.
> 
> 
> 
> 
>   include/linux/ptr_ring.h | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 37b4bb2..6866df4 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
>   
>   /* Note: callers invoking this in a loop must use a compiler barrier,
>    * for example cpu_relax(). Callers must hold producer_lock.
> + * Callers are responsible for making sure pointer that is being queued
> + * points to a valid data.
>    */
>   static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
>   {
>   	if (unlikely(!r->size) || r->queue[r->producer])
>   		return -ENOSPC;
>   
> +	/* Make sure the pointer we are storing points to a valid data. */
> +	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
> +	smp_wmb();
> +
>   	r->queue[r->producer++] = ptr;
>   	if (unlikely(r->producer >= r->size))
>   		r->producer = 0;
> @@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
>   	if (ptr)
>   		__ptr_ring_discard_one(r);
>   
> +	/* Make sure anyone accessing data through the pointer is up to date. */
> +	/* Pairs with smp_wmb in __ptr_ring_produce. */
> +	smp_read_barrier_depends();
>   	return ptr;
>   }
>   
> 

Re: [PATCH] ptr_ring: add barriers

[Michael S. Tsirkin]

On Wed, Dec 06, 2017 at 02:51:41PM +0530, George Cherian wrote:
> Hi Michael,
> 
> 
> On 12/06/2017 12:59 AM, Michael S. Tsirkin wrote:
> > Users of ptr_ring expect that it's safe to give the
> > data structure a pointer and have it be available
> > to consumers, but that actually requires an smb_wmb
> > or a stronger barrier.
> This is not the exact situation we are seeing.

Could you test the patch pls?

> Let me try to explain the situation
> 
> Affected on ARM64 platform.
> 1) tun_net_xmit calls skb_array_produce, which pushes the skb to the
> ptr_ring, this push is protected by a producer_lock.
> 
> 2)Prior to this call the tun_net_xmit calls skb_orphan which calls the
> skb->destructor and sets skb->destructor and skb->sk as NULL.
> 
> 2.a) These 2 writes are getting reordered
> 
> 3) At the same time in the receive side (tun_ring_recv), which gets executed
> in another core calls skb_array_consume which pulls the skb from  ptr ring,
> this pull is protected by a consumer lock.
> 
> 4) eventually calling the skb->destructor (sock_wfree) with stale values.
> 
> Also note that this issue is reproducible in a long run and doesn't happen
> immediately after the launch of multiple VM's (infact the particular test
> cases launches 56 VM's which does iperf back and forth)
> 
> > 
> > In absence of such barriers and on architectures that reorder writes,
> > consumer might read an un=initialized value from an skb pointer stored
> > in the skb array.  This was observed causing crashes.
> > 
> > To fix, add memory barriers.  The barrier we use is a wmb, the
> > assumption being that producers do not need to read the value so we do
> > not need to order these reads.
> It is not the case that producer is reading the value, but the consumer
> reading stale value. So we need to have a strict rmb in place .
> 
> > 
> > Reported-by: George Cherian <george.cherian@cavium.com>
> > Suggested-by: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > George, could you pls report whether this patch fixes
> > the issue for you?
> > 
> > This seems to be needed in stable as well.
> > 
> > 
> > 
> > 
> >   include/linux/ptr_ring.h | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> > 
> > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> > index 37b4bb2..6866df4 100644
> > --- a/include/linux/ptr_ring.h
> > +++ b/include/linux/ptr_ring.h
> > @@ -101,12 +101,18 @@ static inline bool ptr_ring_full_bh(struct ptr_ring *r)
> >   /* Note: callers invoking this in a loop must use a compiler barrier,
> >    * for example cpu_relax(). Callers must hold producer_lock.
> > + * Callers are responsible for making sure pointer that is being queued
> > + * points to a valid data.
> >    */
> >   static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
> >   {
> >   	if (unlikely(!r->size) || r->queue[r->producer])
> >   		return -ENOSPC;
> > +	/* Make sure the pointer we are storing points to a valid data. */
> > +	/* Pairs with smp_read_barrier_depends in __ptr_ring_consume. */
> > +	smp_wmb();
> > +
> >   	r->queue[r->producer++] = ptr;
> >   	if (unlikely(r->producer >= r->size))
> >   		r->producer = 0;
> > @@ -275,6 +281,9 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
> >   	if (ptr)
> >   		__ptr_ring_discard_one(r);
> > +	/* Make sure anyone accessing data through the pointer is up to date. */
> > +	/* Pairs with smp_wmb in __ptr_ring_produce. */
> > +	smp_read_barrier_depends();
> >   	return ptr;
> >   }
> > 

Re: [PATCH] ptr_ring: add barriers

[David Miller]

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Tue, 5 Dec 2017 21:29:37 +0200

> Users of ptr_ring expect that it's safe to give the
> data structure a pointer and have it be available
> to consumers, but that actually requires an smb_wmb
> or a stronger barrier.
> 
> In absence of such barriers and on architectures that reorder writes,
> consumer might read an un=initialized value from an skb pointer stored
> in the skb array.  This was observed causing crashes.
> 
> To fix, add memory barriers.  The barrier we use is a wmb, the
> assumption being that producers do not need to read the value so we do
> not need to order these reads.
> 
> Reported-by: George Cherian <george.cherian@cavium.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> George, could you pls report whether this patch fixes
> the issue for you?
> 
> This seems to be needed in stable as well.

I really need some testing feedback for this before I apply it
and queue it up for -stable.

George?

Re: [PATCH] ptr_ring: add barriers

[David Miller]

From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Tue, 5 Dec 2017 21:29:37 +0200

> Users of ptr_ring expect that it's safe to give the
> data structure a pointer and have it be available
> to consumers, but that actually requires an smb_wmb
> or a stronger barrier.
> 
> In absence of such barriers and on architectures that reorder writes,
> consumer might read an un=initialized value from an skb pointer stored
> in the skb array.  This was observed causing crashes.
> 
> To fix, add memory barriers.  The barrier we use is a wmb, the
> assumption being that producers do not need to read the value so we do
> not need to order these reads.
> 
> Reported-by: George Cherian <george.cherian@cavium.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

I'm asked for asking for testing feedback and did not get it in a
reasonable amount of time.

So I'm applying this as-is, and queueing it up for -stable.

Thank you.

Re: [PATCH] ptr_ring: add barriers

[George Cherian]

Hi David,

On 12/11/2017 09:23 PM, David Miller wrote:
> From: "Michael S. Tsirkin" <mst@redhat.com>
> Date: Tue, 5 Dec 2017 21:29:37 +0200
> 
>> Users of ptr_ring expect that it's safe to give the
>> data structure a pointer and have it be available
>> to consumers, but that actually requires an smb_wmb
>> or a stronger barrier.
>>
>> In absence of such barriers and on architectures that reorder writes,
>> consumer might read an un=initialized value from an skb pointer stored
>> in the skb array.  This was observed causing crashes.
>>
>> To fix, add memory barriers.  The barrier we use is a wmb, the
>> assumption being that producers do not need to read the value so we do
>> not need to order these reads.
>>
>> Reported-by: George Cherian <george.cherian@cavium.com>
>> Suggested-by: Jason Wang <jasowang@redhat.com>
>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> I'm asked for asking for testing feedback and did not get it in a
> reasonable amount of time.
> 
The tests have completed more than 48 hours without any failures.
I won't interrupt the same and run for longer time.
In case of any issue I will report the same.
> So I'm applying this as-is, and queueing it up for -stable.
> 
> Thank you.

Regards,
-George
>