Commit e7169530 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
Browse files

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 a BH, 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: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d4e854cc

include/linux/ptr_ring.h

+31 −5
Original line number Diff line number Diff line
@@ -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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