path: root/net/atm/pppoatm.c
diff options
authorDavid Woodhouse <dwmw2@infradead.org>2018-06-16 11:55:44 +0100
committerDavid S. Miller <davem@davemloft.net>2018-06-17 08:27:01 +0900
commit9bbe60a67be5a1c6f79b3c9be5003481a50529ff (patch)
treec02a003187d3c3a5b2b5db65d3bb9d0bf3bea85e /net/atm/pppoatm.c
parent0841d98641bdb9c7f873adf7f6865ab0880ddfc7 (diff)
atm: Preserve value of skb->truesize when accounting to vcc
ATM accounts for in-flight TX packets in sk_wmem_alloc of the VCC on which they are to be sent. But it doesn't take ownership of those packets from the sock (if any) which originally owned them. They should remain owned by their actual sender until they've left the box. There's a hack in pskb_expand_head() to avoid adjusting skb->truesize for certain skbs, precisely to avoid messing up sk_wmem_alloc accounting. Ideally that hack would cover the ATM use case too, but it doesn't — skbs which aren't owned by any sock, for example PPP control frames, still get their truesize adjusted when the low-level ATM driver adds headroom. This has always been an issue, it seems. The truesize of a packet increases, and sk_wmem_alloc on the VCC goes negative. But this wasn't for normal traffic, only for control frames. So I think we just got away with it, and we probably needed to send 2GiB of LCP echo frames before the misaccounting would ever have caused a problem and caused atm_may_send() to start refusing packets. Commit 14afee4b609 ("net: convert sock.sk_wmem_alloc from atomic_t to refcount_t") did exactly what it was intended to do, and turned this mostly-theoretical problem into a real one, causing PPPoATM to fail immediately as sk_wmem_alloc underflows and atm_may_send() *immediately* starts refusing to allow new packets. The least intrusive solution to this problem is to stash the value of skb->truesize that was accounted to the VCC, in a new member of the ATM_SKB(skb) structure. Then in atm_pop_raw() subtract precisely that value instead of the then-current value of skb->truesize. Fixes: 158f323b9868 ("net: adjust skb->truesize in pskb_expand_head()") Signed-off-by: David Woodhouse <dwmw2@infradead.org> Tested-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/atm/pppoatm.c')
1 files changed, 1 insertions, 2 deletions
diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
index 21d9d341a619..af8c4b38b746 100644
--- a/net/atm/pppoatm.c
+++ b/net/atm/pppoatm.c
@@ -350,8 +350,7 @@ static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
return 1;
- refcount_add(skb->truesize, &sk_atm(ATM_SKB(skb)->vcc)->sk_wmem_alloc);
- ATM_SKB(skb)->atm_options = ATM_SKB(skb)->vcc->atm_options;
+ atm_account_tx(vcc, skb);
skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)