3.18-stable review patch. If anyone has any objections, please let me know.
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From: Gao Feng fgao@ikuai8.com
[ Upstream commit c48367427a39ea0b85c7cf018fe4256627abfd9e ]
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: Gao Feng fgao@ikuai8.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/tcp.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1099,9 +1099,11 @@ void tcp_select_initial_window(int __spa
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 */