From: Magnus Karlsson <magnus.karlsson@intel.com>
Date: Wed, 11 Jul 2018 10:12:50 +0200
Subject: xsk: do not return EAGAIN from sendmsg when completion queue is full
Patch-mainline: v4.18-rc6
Git-commit: 9684f5e7c8cdf076aeec81344d4893a30f7aa6a1
References: bsc#1109837

This patch stops returning EAGAIN in TX copy mode when the completion
queue is full as zero-copy does not do this. Instead this situation
can be detected by comparing the head and tail pointers of the
completion queue in both modes. In any case, EAGAIN was not the
correct error code here since no amount of calling sendmsg will solve
the problem. Only consuming one or more messages on the completion
queue will fix this.

With this patch, the error reporting becomes consistent between copy
mode and zero-copy mode.

Fixes: 35fcde7f8deb ("xsk: support for Tx")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/xdp/xsk.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -233,10 +233,8 @@ static int xsk_generic_xmit(struct sock
 			goto out;
 		}
 
-		if (xskq_reserve_addr(xs->umem->cq)) {
-			err = -EAGAIN;
+		if (xskq_reserve_addr(xs->umem->cq))
 			goto out;
-		}
 
 		len = desc.len;
 		if (unlikely(len > xs->dev->mtu)) {