[ 001/123] net: fix a race in gro_cell_poll()

Greg Kroah-Hartman
2013-01-09T21:59:51Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit f8e8f97c11d5ff3cc47d85b97c7c35e443dcf490 ]

Dmitry Kravkov reported packet drops for GRE packets since GRO support
was added.

There is a race in gro_cell_poll() because we call napi_complete()
without any synchronization with a concurrent gro_cells_receive()

Once bug was triggered, we queued packets but did not schedule NAPI
poll.

We can fix this issue using the spinlock protected the napi_skbs queue,
as we have to hold it to perform skb dequeue anyway.

As we open-code skb_dequeue(), we no longer need to mask IRQS, as both
producer and consumer run under BH context.

Bug added in commit c9e6bc644e (net: add gro_cells infrastructure)

Reported-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/gro_cells.h | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

--- a/include/net/gro_cells.h
+++ b/include/net/gro_cells.h
@@ -17,7 +17,6 @@ struct gro_cells {

static inline void gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb)
{
- unsigned long flags;
struct gro_cell *cell = gcells->cells;
struct net_device *dev = skb->dev;

@@ -35,32 +34,37 @@ static inline void gro_cells_receive(str
return;
}

- spin_lock_irqsave(&cell->napi_skbs.lock, flags);
+ /* We run in BH context */
+ spin_lock(&cell->napi_skbs.lock);

__skb_queue_tail(&cell->napi_skbs, skb);
if (skb_queue_len(&cell->napi_skbs) == 1)
napi_schedule(&cell->napi);

- spin_unlock_irqrestore(&cell->napi_skbs.lock, flags);
+ spin_unlock(&cell->napi_skbs.lock);
}

+/* called unser BH context */
static inline int gro_cell_poll(struct napi_struct *napi, int budget)
{
struct gro_cell *cell = container_of(napi, struct gro_cell, napi);
struct sk_buff *skb;
int work_done = 0;

+ spin_lock(&cell->napi_skbs.lock);
while (work_done < budget) {
- skb = skb_dequeue(&cell->napi_skbs);
+ skb = __skb_dequeue(&cell->napi_skbs);
if (!skb)
break;
-
+ spin_unlock(&cell->napi_skbs.lock);
napi_gro_receive(napi, skb);
work_done++;
+ spin_lock(&cell->napi_skbs.lock);
}

if (work_done < budget)
napi_complete(napi);
+ spin_unlock(&cell->napi_skbs.lock);
return work_done;
}