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net-tcp_bbr: v2: don't assume prior_cwnd was set entering CA_Loss
Fix WARN_ON_ONCE() warnings that were firing and pointing to a bbr->prior_cwnd of 0 when exiting CA_Loss and transitioning to CA_Open. The issue was that tcp_simple_retransmit() calls: tcp_set_ca_state(sk, TCP_CA_Loss); without first calling icsk_ca_ops->ssthresh(sk) (because tcp_simple_retransmit() is dealing with losses due to MTU issues and not congestion). The lack of this callback means that BBR did not get a chance to set bbr->prior_cwnd, and thus upon exiting CA_Loss in such cases the WARN_ON_ONCE() would fire due to a zero bbr->prior_cwnd. This commit removes that warning, since a bbr->prior_cwnd of 0 is a valid situation in this state transition. For setting inflight_lo upon entering CA_Loss, to avoid setting an inflight_lo of 0 in this case, this commit switches to taking the max of cwnd and prior_cwnd. We plan to remove that line of code when we switch to cautious (PRR-style) recovery, so that awkwardness will go away. Change-Id: I575dce871c2f20e91e3e9449e1706f42a07b8118 Signed-off-by: Alexandre Frade <kernel@xanmod.org>
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