Commit 48611c47 authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
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[TCP]: Fix fastpath_cnt_hint when GSO skb is partially ACKed

When only GSO skb was partially ACKed, no hints are reset,
therefore fastpath_cnt_hint must be tweaked too or else it can
corrupt fackets_out. The corruption to occur, one must have
non-trivial ACK/SACK sequence, so this bug is not very often
that harmful. There's a fackets_out state reset in TCP because
fackets_out is known to be inaccurate and that fixes the issue
eventually anyway.

In case there was also at least one skb that got fully ACKed,
the fastpath_skb_hint is set to NULL which causes a recount for
fastpath_cnt_hint (the old value won't be accessed anymore),
thus it can safely be decremented without additional checking.

Reported by Cedric Le Goater <>
Signed-off-by: default avatarIlpo Järvinen <>
Signed-off-by: default avatarDavid S. Miller <>
parent 3eb215de
......@@ -2420,6 +2420,9 @@ static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
__u32 dval = min(tp->fackets_out, packets_acked);
tp->fackets_out -= dval;
/* hint's skb might be NULL but we don't need to care */
tp->fastpath_cnt_hint -= min_t(u32, packets_acked,
tp->packets_out -= packets_acked;
BUG_ON(tcp_skb_pcount(skb) == 0);
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