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[PATCH RFC] ptr_ring: fix race conditions when resizing

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  [PATCH RFC] ptr_ring: fix race conditions when resizing "Michael S. Tsirkin" <mst@redhat.com> - 2017-02-10 23:40 +0100
    Re: [PATCH RFC] ptr_ring: fix race conditions when resizing Jason Wang <jasowang@redhat.com> - 2017-02-13 06:10 +0100

#1578836 — [PATCH RFC] ptr_ring: fix race conditions when resizing

Resizing currently drops consumer lock.  This can cause entries to be
reordered, which isn't good in itself.  More importantly, consumer can
detect a false ring empty condition and block forever.

Further, nesting of consumer within producer lock is problematic for
tun, since it produces entries in an interrupt, which causes a
lock order reversal:

       CPU0                    CPU1
       ----                    ----
  consume:
  lock(&(&r->consumer_lock)->rlock);
                               resize:
                               local_irq_disable();
                               lock(&(&r->producer_lock)->rlock);
                               lock(&(&r->consumer_lock)->rlock);
  <Interrupt>
  produce:
  lock(&(&r->producer_lock)->rlock);

To fix, nest producer lock within consumer lock during resize,
and keep consumer lock during the whole swap operation.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/linux/ptr_ring.h | 36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 2052011..6c70444 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -111,6 +111,11 @@ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
 	return 0;
 }
 
+/*
+ * Note: resize (below) nests producer lock within consumer lock, so if you
+ * consume in interrupt or BH context, you must disable interrupts/BH when
+ * calling this.
+ */
 static inline int ptr_ring_produce(struct ptr_ring *r, void *ptr)
 {
 	int ret;
@@ -242,6 +247,11 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
 	return ptr;
 }
 
+/*
+ * Note: resize (below) nests producer lock within consumer lock, so if you
+ * call this in interrupt or BH context, you must disable interrupts/BH when
+ * producing.
+ */
 static inline void *ptr_ring_consume(struct ptr_ring *r)
 {
 	void *ptr;
@@ -357,7 +367,7 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
 	void **old;
 	void *ptr;
 
-	while ((ptr = ptr_ring_consume(r)))
+	while ((ptr = __ptr_ring_consume(r)))
 		if (producer < size)
 			queue[producer++] = ptr;
 		else if (destroy)
@@ -372,6 +382,12 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
 	return old;
 }
 
+/*
+ * Note: producer lock is nested within consumer lock, so if you
+ * resize you must make sure all uses nest correctly.
+ * In particular if you consume ring in interrupt or BH context, you must
+ * disable interrupts/BH when doing so.
+ */
 static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
 				  void (*destroy)(void *))
 {
@@ -382,17 +398,25 @@ static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
 	if (!queue)
 		return -ENOMEM;
 
-	spin_lock_irqsave(&(r)->producer_lock, flags);
+	spin_lock_irqsave(&(r)->consumer_lock, flags);
+	spin_lock(&(r)->producer_lock);
 
 	old = __ptr_ring_swap_queue(r, queue, size, gfp, destroy);
 
-	spin_unlock_irqrestore(&(r)->producer_lock, flags);
+	spin_unlock(&(r)->producer_lock);
+	spin_unlock_irqrestore(&(r)->consumer_lock, flags);
 
 	kfree(old);
 
 	return 0;
 }
 
+/*
+ * Note: producer lock is nested within consumer lock, so if you
+ * resize you must make sure all uses nest correctly.
+ * In particular if you consume ring in interrupt or BH context, you must
+ * disable interrupts/BH when doing so.
+ */
 static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
 					   int size,
 					   gfp_t gfp, void (*destroy)(void *))
@@ -412,10 +436,12 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
 	}
 
 	for (i = 0; i < nrings; ++i) {
-		spin_lock_irqsave(&(rings[i])->producer_lock, flags);
+		spin_lock_irqsave(&(rings[i])->consumer_lock, flags);
+		spin_lock(&(rings[i])->producer_lock);
 		queues[i] = __ptr_ring_swap_queue(rings[i], queues[i],
 						  size, gfp, destroy);
-		spin_unlock_irqrestore(&(rings[i])->producer_lock, flags);
+		spin_unlock(&(rings[i])->producer_lock);
+		spin_unlock_irqrestore(&(rings[i])->consumer_lock, flags);
 	}
 
 	for (i = 0; i < nrings; ++i)
-- 
MST

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#1579411

On 2017年02月11日 06:31, Michael S. Tsirkin wrote:
> Resizing currently drops consumer lock.  This can cause entries to be
> reordered, which isn't good in itself.  More importantly, consumer can
> detect a false ring empty condition and block forever.
>
> Further, nesting of consumer within producer lock is problematic for
> tun, since it produces entries in an interrupt, which causes a

In an bh actually?

Except for this.

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

> lock order reversal:
>
>         CPU0                    CPU1
>         ----                    ----
>    consume:
>    lock(&(&r->consumer_lock)->rlock);
>                                 resize:
>                                 local_irq_disable();
>                                 lock(&(&r->producer_lock)->rlock);
>                                 lock(&(&r->consumer_lock)->rlock);
>    <Interrupt>
>    produce:
>    lock(&(&r->producer_lock)->rlock);
>
> To fix, nest producer lock within consumer lock during resize,
> and keep consumer lock during the whole swap operation.
>
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: stable@vger.kernel.org
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>   include/linux/ptr_ring.h | 36 +++++++++++++++++++++++++++++++-----
>   1 file changed, 31 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 2052011..6c70444 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -111,6 +111,11 @@ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
>   	return 0;
>   }
>   
> +/*
> + * Note: resize (below) nests producer lock within consumer lock, so if you
> + * consume in interrupt or BH context, you must disable interrupts/BH when
> + * calling this.
> + */
>   static inline int ptr_ring_produce(struct ptr_ring *r, void *ptr)
>   {
>   	int ret;
> @@ -242,6 +247,11 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
>   	return ptr;
>   }
>   
> +/*
> + * Note: resize (below) nests producer lock within consumer lock, so if you
> + * call this in interrupt or BH context, you must disable interrupts/BH when
> + * producing.
> + */
>   static inline void *ptr_ring_consume(struct ptr_ring *r)
>   {
>   	void *ptr;
> @@ -357,7 +367,7 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
>   	void **old;
>   	void *ptr;
>   
> -	while ((ptr = ptr_ring_consume(r)))
> +	while ((ptr = __ptr_ring_consume(r)))
>   		if (producer < size)
>   			queue[producer++] = ptr;
>   		else if (destroy)
> @@ -372,6 +382,12 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
>   	return old;
>   }
>   
> +/*
> + * Note: producer lock is nested within consumer lock, so if you
> + * resize you must make sure all uses nest correctly.
> + * In particular if you consume ring in interrupt or BH context, you must
> + * disable interrupts/BH when doing so.
> + */
>   static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
>   				  void (*destroy)(void *))
>   {
> @@ -382,17 +398,25 @@ static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
>   	if (!queue)
>   		return -ENOMEM;
>   
> -	spin_lock_irqsave(&(r)->producer_lock, flags);
> +	spin_lock_irqsave(&(r)->consumer_lock, flags);
> +	spin_lock(&(r)->producer_lock);
>   
>   	old = __ptr_ring_swap_queue(r, queue, size, gfp, destroy);
>   
> -	spin_unlock_irqrestore(&(r)->producer_lock, flags);
> +	spin_unlock(&(r)->producer_lock);
> +	spin_unlock_irqrestore(&(r)->consumer_lock, flags);
>   
>   	kfree(old);
>   
>   	return 0;
>   }
>   
> +/*
> + * Note: producer lock is nested within consumer lock, so if you
> + * resize you must make sure all uses nest correctly.
> + * In particular if you consume ring in interrupt or BH context, you must
> + * disable interrupts/BH when doing so.
> + */
>   static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
>   					   int size,
>   					   gfp_t gfp, void (*destroy)(void *))
> @@ -412,10 +436,12 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
>   	}
>   
>   	for (i = 0; i < nrings; ++i) {
> -		spin_lock_irqsave(&(rings[i])->producer_lock, flags);
> +		spin_lock_irqsave(&(rings[i])->consumer_lock, flags);
> +		spin_lock(&(rings[i])->producer_lock);
>   		queues[i] = __ptr_ring_swap_queue(rings[i], queues[i],
>   						  size, gfp, destroy);
> -		spin_unlock_irqrestore(&(rings[i])->producer_lock, flags);
> +		spin_unlock(&(rings[i])->producer_lock);
> +		spin_unlock_irqrestore(&(rings[i])->consumer_lock, flags);
>   	}
>   
>   	for (i = 0; i < nrings; ++i)

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