[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 <clg@fr.ibm.com> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Adrian Bunk <bunk@kernel.org>
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