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Commit c4836742 authored by Gao Feng's avatar Gao Feng Committed by David S. Miller
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tcp: sysctl: Fix a race to avoid unexpected 0 window from space 



Because sysctl_tcp_adv_win_scale could be changed any time, so there
is one race in tcp_win_from_space.
For example,
1.sysctl_tcp_adv_win_scale<=0 (sysctl_tcp_adv_win_scale is negative now)
2.space>>(-sysctl_tcp_adv_win_scale) (sysctl_tcp_adv_win_scale is postive now)

As a result, tcp_win_from_space returns 0. It is unexpected.

Certainly if the compiler put the sysctl_tcp_adv_win_scale into one
register firstly, then use the register directly, it would be ok.
But we could not depend on the compiler behavior.

Signed-off-by: default avatarGao Feng <fgao@ikuai8.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e013fb7c

include/net/tcp.h

+5 −3
Original line number Diff line number Diff line
@@ -1248,9 +1248,11 @@ void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd, 


static inline int tcp_win_from_space(int space)

{

	return sysctl_tcp_adv_win_scale<=0 ?

		(space>>(-sysctl_tcp_adv_win_scale)) :

		space - (space>>sysctl_tcp_adv_win_scale);

	int tcp_adv_win_scale = sysctl_tcp_adv_win_scale;



	return tcp_adv_win_scale <= 0 ?

		(space>>(-tcp_adv_win_scale)) :

		space - (space>>tcp_adv_win_scale);

}



/* Note: caller must be prepared to deal with negative returns */