netdev - [PATCH bpf-next 6/8] xsk: add missing write- and data-dependency barrier

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Message-Id: <20180522073503.2199-7-bjorn.topel@gmail.com>
Date:   Tue, 22 May 2018 09:35:01 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     magnus.karlsson@...el.com, magnus.karlsson@...il.com, ast@...com,
        daniel@...earbox.net, netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>
Subject: [PATCH bpf-next 6/8] xsk: add missing write- and data-dependency barrier

From: Björn Töpel <bjorn.topel@...el.com>

Here, we add a missing write-barrier, and use READ_ONCE for the
data-dependency barrier.

Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
---
 net/xdp/xsk.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 378dd9287da5..01f010ec0c05 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -228,6 +228,8 @@ static int xsk_init_queue(u32 entries, struct xsk_queue **queue,
 	if (!q)
 		return -ENOMEM;
 
+	/* Make sure queue is ready before it can be seen by others */
+	smp_wmb();
 	*queue = q;
 	return 0;
 }
@@ -532,21 +534,23 @@ static int xsk_mmap(struct file *file, struct socket *sock,
 	unsigned long size = vma->vm_end - vma->vm_start;
 	struct xdp_sock *xs = xdp_sk(sock->sk);
 	struct xsk_queue *q = NULL;
+	struct xdp_umem *umem;
 	unsigned long pfn;
 	struct page *qpg;
 
 	if (offset == XDP_PGOFF_RX_RING) {
-		q = xs->rx;
+		q = READ_ONCE(xs->rx);
 	} else if (offset == XDP_PGOFF_TX_RING) {
-		q = xs->tx;
+		q = READ_ONCE(xs->tx);
 	} else {
-		if (!xs->umem)
+		umem = READ_ONCE(xs->umem);
+		if (!umem)
 			return -EINVAL;
 
 		if (offset == XDP_UMEM_PGOFF_FILL_RING)
-			q = xs->umem->fq;
+			q = READ_ONCE(umem->fq);
 		else if (offset == XDP_UMEM_PGOFF_COMPLETION_RING)
-			q = xs->umem->cq;
+			q = READ_ONCE(umem->cq);
 	}
 
 	if (!q)
-- 
2.14.1