netdev - [PATCH bpf] net: xsk: don't return frames via the allocator on error

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Message-Id: <20180728032008.23402-1-jakub.kicinski@netronome.com>
Date:   Fri, 27 Jul 2018 20:20:08 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     alexei.starovoitov@...il.com, daniel@...earbox.net
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org,
        bjorn.topel@...el.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCH bpf] net: xsk: don't return frames via the allocator on error

xdp_return_buff() is used when frame has been successfully
handled (transmitted) or if an error occurred during delayed
processing and there is no way to report it back to
xdp_do_redirect().

In case of __xsk_rcv_zc() error is propagated all the way
back to the driver, so there is no need to call
xdp_return_buff().  Driver will recycle the frame anyway
after seeing that error happened.

Fixes: 173d3adb6f43 ("xsk: add zero-copy support for Rx")
Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
Patch could as well be applied to bpf-next, since there are no drivers
for AF_XDP in tree, yet.  xdp_umem_get_dma() and xdp_umem_get_data() are
not even exported.  But one could reimplent those...  

As I mentioned I think this makes the entire MEM_TYPE_ZERO_COPY allocator
handling dead code now :(

 net/xdp/xsk.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 72335c2e8108..4e937cd7c17d 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -84,10 +84,8 @@ static int __xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
 {
 	int err = xskq_produce_batch_desc(xs->rx, (u64)xdp->handle, len);
 
-	if (err) {
-		xdp_return_buff(xdp);
+	if (err)
 		xs->rx_dropped++;
-	}
 
 	return err;
 }
-- 
2.17.1