On 2019/8/6 8:46, Jakub Kicinski wrote:
> On Sat, 3 Aug 2019 20:31:39 +0800, Jiangfeng Xiao wrote:
>> If hip04_tx_reclaim is interrupted while it is running
>> and then __napi_schedule continues to execute
>> hip04_rx_poll->hip04_tx_reclaim, reentrancy occurs
>> and oops is generated. So you need to mask the interrupt
>> during the hip04_tx_reclaim run.
>
> Napi poll method for the same napi instance can't be run concurrently.
> Could you explain a little more what happens here?
>
Because netif_napi_add(ndev, &priv->napi, hip04_rx_poll, NAPI_POLL_WEIGHT);
So hip04_rx_poll is a napi instance.
I did not say that hip04_rx_poll has reentered.
I am talking about the reentrant of hip04_tx_reclaim.
Pre-modification code:
static int hip04_rx_poll(struct napi_struct *napi, int budget)
{
[...]
/* enable rx interrupt */
writel_relaxed(priv->reg_inten, priv->base + PPE_INTEN);
napi_complete_done(napi, rx);
done:
/* clean up tx descriptors and start a new timer if necessary */
tx_remaining = hip04_tx_reclaim(ndev, false);
[...]
}
hip04_tx_reclaim is executed after "enable rx interrupt" and napi_complete_done.
If hip04_tx_reclaim is interrupted while it is running, and then
__irq_svc->gic_handle_irq->hip04_mac_interrupt->__napi_schedule->hip04_rx_poll->hip04_tx_reclaim
Also looking at hip04_tx_reclaim
static int hip04_tx_reclaim(struct net_device *ndev, bool force)
{
[1] struct hip04_priv *priv = netdev_priv(ndev);
[2] unsigned tx_tail = priv->tx_tail;
[3] [...]
[4] bytes_compl += priv->tx_skb[tx_tail]->len;
[5] dev_kfree_skb(priv->tx_skb[tx_tail]);
[6] priv->tx_skb[tx_tail] = NULL;
[7] tx_tail = TX_NEXT(tx_tail);
[8] [...]
[9] priv->tx_tail = tx_tail;
}
An interrupt occurs if hip04_tx_reclaim just executes to the line 6,
priv->tx_skb[tx_tail] is NULL, and then
__irq_svc->gic_handle_irq->hip04_mac_interrupt->__napi_schedule->hip04_rx_poll->hip04_tx_reclaim
Then hip04_tx_reclaim will handle kernel NULL pointer dereference on line 4.
A reentrant occurs in hip04_tx_reclaim and oops is generated.
My commit is to execute hip04_tx_reclaim before "enable rx interrupt" and
napi_complete_done.
Then hip04_tx_reclaim can also be protected by the napi poll method so that no
reentry occurs.
thanks.
