The above referenced commit has problems on older non-rbTree kernels.
AFAICS, the commit has only been backported to 4.14 up to now, but the commit that fdfc5c8594c2 is fixing (namely ce5ec440994b ("tcp: ensure epoll edge trigger wakeup when write queue is empty"), is in v4.2.
Christoph Paasch (2): tcp: Reset send_head when removing skb from write-queue tcp: Don't dequeue SYN/FIN-segments from write-queue
net/ipv4/tcp.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)