netdev - [PATCH bpf-next v3 1/4] xsk: avoid store-tearing when assigning queues

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Message-Id: <20190904114913.17217-2-bjorn.topel@gmail.com>
Date:   Wed,  4 Sep 2019 13:49:10 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, magnus.karlsson@...il.com,
        bpf@...r.kernel.org, jonathan.lemon@...il.com,
        syzbot+c82697e3043781e08802@...kaller.appspotmail.com,
        hdanton@...a.com, i.maximets@...sung.com
Subject: [PATCH bpf-next v3 1/4] xsk: avoid store-tearing when assigning queues

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

Use WRITE_ONCE when doing the store of tx, rx, fq, and cq, to avoid
potential store-tearing. These members are read outside of the control
mutex in the mmap implementation.

Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>
Fixes: 37b076933a8e ("xsk: add missing write- and data-dependency barrier")
Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
---
 net/xdp/xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 187fd157fcff..271d8d3fb11e 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -434,7 +434,7 @@ static int xsk_init_queue(u32 entries, struct xsk_queue **queue,
 
 	/* Make sure queue is ready before it can be seen by others */
 	smp_wmb();
-	*queue = q;
+	WRITE_ONCE(*queue, q);
 	return 0;
 }
 
-- 
2.20.1