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authorNeal Cardwell <ncardwell@google.com>2016-01-25 14:01:53 -0800
committerDavid S. Miller <davem@davemloft.net>2016-01-28 16:02:48 -0800
commitd88270eef4b56bd7973841dd1fed387ccfa83709 (patch)
tree9be6ebbcc863d352917a0c26582e850ec4917674 /drivers/net/ethernet/ezchip/Kconfig
parentinet: frag: Always orphan skbs inside ip_defrag() (diff)
downloadlinux-dev-d88270eef4b56bd7973841dd1fed387ccfa83709.tar.xz
linux-dev-d88270eef4b56bd7973841dd1fed387ccfa83709.zip
tcp: fix tcp_mark_head_lost to check skb len before fragmenting
This commit fixes a corner case in tcp_mark_head_lost() which was causing the WARN_ON(len > skb->len) in tcp_fragment() to fire. tcp_mark_head_lost() was assuming that if a packet has tcp_skb_pcount(skb) of N, then it's safe to fragment off a prefix of M*mss bytes, for any M < N. But with the tricky way TCP pcounts are maintained, this is not always true. For example, suppose the sender sends 4 1-byte packets and have the last 3 packet sacked. It will merge the last 3 packets in the write queue into an skb with pcount = 3 and len = 3 bytes. If another recovery happens after a sack reneging event, tcp_mark_head_lost() may attempt to split the skb assuming it has more than 2*MSS bytes. This sounds very counterintuitive, but as the commit description for the related commit c0638c247f55 ("tcp: don't fragment SACKed skbs in tcp_mark_head_lost()") notes, this is because tcp_shifted_skb() coalesces adjacent regions of SACKed skbs, and when doing this it preserves the sum of their packet counts in order to reflect the real-world dynamics on the wire. The c0638c247f55 commit tried to avoid problems by not fragmenting SACKed skbs, since SACKed skbs are where the non-proportionality between pcount and skb->len/mss is known to be possible. However, that commit did not handle the case where during a reneging event one of these weird SACKed skbs becomes an un-SACKed skb, which tcp_mark_head_lost() can then try to fragment. The fix is to simply mark the entire skb lost when this happens. This makes the recovery slightly more aggressive in such corner cases before we detect reordering. But once we detect reordering this code path is by-passed because FACK is disabled. Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/ethernet/ezchip/Kconfig')
0 files changed, 0 insertions, 0 deletions