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: Dmitry Vyukov <dvyukov@google.com> Cc: stable@vger.kernel.org Cc: "David S. Miller" <davem@davemloft.net> Acked-by: Jason Wang <jasowang@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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d4e854ccd6
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@ -111,6 +111,11 @@ static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
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return 0;
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}
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/*
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* Note: resize (below) nests producer lock within consumer lock, so if you
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* consume in interrupt or BH context, you must disable interrupts/BH when
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* calling this.
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*/
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static inline int ptr_ring_produce(struct ptr_ring *r, void *ptr)
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{
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int ret;
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@ -242,6 +247,11 @@ static inline void *__ptr_ring_consume(struct ptr_ring *r)
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return ptr;
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}
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/*
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* Note: resize (below) nests producer lock within consumer lock, so if you
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* call this in interrupt or BH context, you must disable interrupts/BH when
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* producing.
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*/
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static inline void *ptr_ring_consume(struct ptr_ring *r)
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{
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void *ptr;
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@ -357,7 +367,7 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
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void **old;
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void *ptr;
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while ((ptr = ptr_ring_consume(r)))
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while ((ptr = __ptr_ring_consume(r)))
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if (producer < size)
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queue[producer++] = ptr;
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else if (destroy)
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@ -372,6 +382,12 @@ static inline void **__ptr_ring_swap_queue(struct ptr_ring *r, void **queue,
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return old;
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}
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/*
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* Note: producer lock is nested within consumer lock, so if you
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* resize you must make sure all uses nest correctly.
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* In particular if you consume ring in interrupt or BH context, you must
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* disable interrupts/BH when doing so.
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*/
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static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
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void (*destroy)(void *))
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{
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@ -382,17 +398,25 @@ static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
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if (!queue)
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return -ENOMEM;
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spin_lock_irqsave(&(r)->producer_lock, flags);
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spin_lock_irqsave(&(r)->consumer_lock, flags);
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spin_lock(&(r)->producer_lock);
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old = __ptr_ring_swap_queue(r, queue, size, gfp, destroy);
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spin_unlock_irqrestore(&(r)->producer_lock, flags);
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spin_unlock(&(r)->producer_lock);
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spin_unlock_irqrestore(&(r)->consumer_lock, flags);
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kfree(old);
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return 0;
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}
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/*
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* Note: producer lock is nested within consumer lock, so if you
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* resize you must make sure all uses nest correctly.
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* In particular if you consume ring in interrupt or BH context, you must
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* disable interrupts/BH when doing so.
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*/
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static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
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int size,
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gfp_t gfp, void (*destroy)(void *))
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@ -412,10 +436,12 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings, int nrings,
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}
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for (i = 0; i < nrings; ++i) {
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spin_lock_irqsave(&(rings[i])->producer_lock, flags);
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spin_lock_irqsave(&(rings[i])->consumer_lock, flags);
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spin_lock(&(rings[i])->producer_lock);
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queues[i] = __ptr_ring_swap_queue(rings[i], queues[i],
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size, gfp, destroy);
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spin_unlock_irqrestore(&(rings[i])->producer_lock, flags);
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spin_unlock(&(rings[i])->producer_lock);
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spin_unlock_irqrestore(&(rings[i])->consumer_lock, flags);
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}
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for (i = 0; i < nrings; ++i)
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