Messages in this thread | | | Date | Mon, 21 Oct 2019 10:37:31 +0200 | From | Steffen Klassert <> | Subject | Re: [PATCH] xfrm : lock input tasklet skb queue |
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On Sun, Oct 20, 2019 at 08:46:10AM -0700, Tom Rix wrote: > On PREEMPT_RT_FULL while running netperf, a corruption > of the skb queue causes an oops. > > This appears to be caused by a race condition here > __skb_queue_tail(&trans->queue, skb); > tasklet_schedule(&trans->tasklet); > Where the queue is changed before the tasklet is locked by > tasklet_schedule. > > The fix is to use the skb queue lock. > > Signed-off-by: Tom Rix <trix@redhat.com> > --- > net/xfrm/xfrm_input.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c > index 9b599ed66d97..226dead86828 100644 > --- a/net/xfrm/xfrm_input.c > +++ b/net/xfrm/xfrm_input.c > @@ -758,12 +758,16 @@ static void xfrm_trans_reinject(unsigned long data) > struct xfrm_trans_tasklet *trans = (void *)data; > struct sk_buff_head queue; > struct sk_buff *skb; > + unsigned long flags; > > __skb_queue_head_init(&queue); > + spin_lock_irqsave(&trans->queue.lock, flags); > skb_queue_splice_init(&trans->queue, &queue); > > while ((skb = __skb_dequeue(&queue))) > XFRM_TRANS_SKB_CB(skb)->finish(dev_net(skb->dev), NULL, skb); > + > + spin_unlock_irqrestore(&trans->queue.lock, flags); > } > > int xfrm_trans_queue(struct sk_buff *skb, > @@ -771,15 +775,20 @@ int xfrm_trans_queue(struct sk_buff *skb, > struct sk_buff *)) > { > struct xfrm_trans_tasklet *trans; > + unsigned long flags; > > trans = this_cpu_ptr(&xfrm_trans_tasklet); > + spin_lock_irqsave(&trans->queue.lock, flags);
As you can see above 'trans' is per cpu, so a spinlock is not needed here. Also this does not run in hard interrupt context, so irqsave is also not needed. I don't see how this can fix anything.
Can you please explain that race a bit more detailed?
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