From: "Sam Jansen" <sjansen@google.com>

sysctl_tcp_congestion_control seems to have a bug that prevents it
from actually calling the tcp_set_default_congestion_control
function. This is not so apparent because it does not return an error
and generally the /proc interface is used to configure the default TCP
congestion control algorithm.  This is present in 2.6.18 onwards and
probably earlier, though I have not inspected 2.6.15--2.6.17.

sysctl_tcp_congestion_control calls sysctl_string and expects a successful
return code of 0. In such a case it actually sets the congestion control
algorithm with tcp_set_default_congestion_control. Otherwise, it returns the
value returned by sysctl_string. This was correct in 2.6.14, as sysctl_string
returned 0 on success. However, sysctl_string was updated to return 1 on
success around about 2.6.15 and sysctl_tcp_congestion_control was not updated.
Even though sysctl_tcp_congestion_control returns 1, do_sysctl_strategy
converts this return code to '0', so the caller never notices the error.
Signed-off-by: David S. Miller <davem@davemloft.net>