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SubjectRe: [PATCH RFC] ptr_ring: fix race conditions when resizing
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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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