author Neal Cardwell email@example.com 2012-01-28 17:29:46 (GMT)
committer David S. Miller firstname.lastname@example.org 2012-01-30 17:42:58 (GMT)
commit 5b35e1e6e9ca651e6b291c96d1106043c9af314a (patch)
parent 4acb41903b2f99f3dffd4c3df9acc84ca5942cb2 (diff)
tcp: fix tcp_trim_head() to adjust segment count with skb MSS
This commit fixes tcp_trim_head() to recalculate the number of segments in the skb with the skb’s existing MSS, so trimming the head causes the skb segment count to be monotonically non-increasing - it should stay the same or go down, but not increase.
Previously tcp_trim_head() used the current MSS of the connection. But if there was a decrease in MSS between original transmission and ACK (e.g. due to PMTUD), this could cause tcp_trim_head() to counter-intuitively increase the segment count when trimming bytes off the head of an skb. This violated assumptions in tcp_tso_acked() that tcp_trim_head() only decreases the packet count, so that packets_acked in tcp_tso_acked() could underflow, leading tcp_clean_rtx_queue() to pass u32 pkts_acked values as large as 0xffffffff to ca_ops->pkts_acked().
As an aside, if tcp_trim_head() had really wanted the skb to reflect the current MSS, it should have called tcp_set_skb_tso_segs() unconditionally, since a decrease in MSS would mean that a single-packet skb should now be sliced into multiple segments.
1 files changed, 2 insertions, 4 deletions
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