Re: TCP stops sending packets over loopback on 4.10-rc3?

On Wed, 2017-01-25 at 09:14 -0500, Josef Bacik wrote:

On Tue, Jan 24, 2017 at 9:07 AM, Eric Dumazet [off-list ref] 

quoted

git grep -n SOCK_QUEUE_SHRUNK

-> tcp_check_space()

But tcp_check_space() doesn't actually reduce sk_wmem_queued from what 
I can see.  The only places that appear to reduce it are tcp_trim_head, 
which is only called in the retransmit path, and sk_wmem_free_skb, 
which seems to be right,

This is exactly how it works.

We free a bunch of skbs (an ACK can acknowledge dozens of them), and set
the SOCK_QUEUE_SHRUNK.

Then later, tcp_check_space() is called once and check if the bit was
set by a prior call to tcp_trim_head() or full skb freeing.

 but I added a trace_printk() in it to see if 
it was firing during my test and it never fires.  So we _appear_ to 
only ever be incrementing this counter, but never decrementing it.  I'm 
doing a bunch of tracing trying to figure out what is going on here but 
so far nothing is popping which is starting to make me think ftrace is 
broken.  Thanks,

Just to make sure, are you telling use native/standard TCP is broken
over loopback, or is that only when using an additional kernel module ?