path: root/arch/sh64/oprofile
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authorPatrick McHardy <kaber@trash.net>2008-07-14 21:09:22 +0300
committerAdrian Bunk <bunk@kernel.org>2008-07-14 21:09:22 +0300
commitb9954f3d67c9f9e8611ec6c94955eecc0e309a26 (patch)
treec02631d3c3b7d871e8bc5f714f9f3dfe061a875d /arch/sh64/oprofile
parent69731ebbb3d2283c2c33a2bf262d785e2362b876 (diff)
TCP: Fix shrinking windows with window scaling
Upstream commit: 607bfbf2d55dd1cfe5368b41c2a81a8c9ccf4723 When selecting a new window, tcp_select_window() tries not to shrink the offered window by using the maximum of the remaining offered window size and the newly calculated window size. The newly calculated window size is always a multiple of the window scaling factor, the remaining window size however might not be since it depends on rcv_wup/rcv_nxt. This means we're effectively shrinking the window when scaling it down. The dump below shows the problem (scaling factor 2^7): - Window size of 557 (71296) is advertised, up to 3111907257: IP > . ack 3111835961 win 557 <...> - New window size of 514 (65792) is advertised, up to 3111907217, 40 bytes below the last end: IP > . 3113575668:3113577116(1448) ack 3111841425 win 514 <...> The number 40 results from downscaling the remaining window: 3111907257 - 3111841425 = 65832 65832 / 2^7 = 514 65832 % 2^7 = 40 If the sender uses up the entire window before it is shrunk, this can have chaotic effects on the connection. When sending ACKs, tcp_acceptable_seq() will notice that the window has been shrunk since tcp_wnd_end() is before tp->snd_nxt, which makes it choose tcp_wnd_end() as sequence number. This will fail the receivers checks in tcp_sequence() however since it is before it's tp->rcv_wup, making it respond with a dupack. If both sides are in this condition, this leads to a constant flood of ACKs until the connection times out. Make sure the window is never shrunk by aligning the remaining window to the window scaling factor. Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Adrian Bunk <bunk@kernel.org>
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