Do we need ACCESS_ONCE() here to avoid check/use issues?
-----Original Message-----
From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com]
Sent: Wednesday, October 19, 2016 2:53 PM
To: net...@vger.kernel.org
Cc: Stephen Hemminger <sthem...@microsoft.com>; de...@linuxdriverproject.org;
linux-ker...@vger.kernel.org; KY Srinivasan <k...@microsoft.com>; Haiyang Zhang
<haiya...@microsoft.com>
Subject: [PATCH net-next] hv_netvsc: fix a race between netvsc_send() and
netvsc_init_buf()
Fix in commit 880988348270 ("hv_netvsc: set nvdev link after populating
chn_table") turns out to be incomplete. A crash in
netvsc_get_next_send_section() is observed on mtu change when the device is
under load. The race I identified is: if we get to netvsc_send() after we set
net_device_ctx->nvdev link in netvsc_device_add() but before we finish
netvsc_connect_vsp()->netvsc_init_buf() send_section_map is not allocated and
we crash. Unfortunately we can't set net_device_ctx->nvdev link after the
netvsc_init_buf() call as during the negotiation we need to receive packets and
on the receive path we check for it. It would probably be possible to split
nvdev into a pair of nvdev_in and nvdev_out links and check them accordingly in
get_outbound_net_device()/
get_inbound_net_device() but this looks like an overkill.
Check that send_section_map is allocated in netvsc_send().
Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
drivers/net/hyperv/netvsc.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c index
720b5fa..e2bfaac 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -888,6 +888,13 @@ int netvsc_send(struct hv_device *device,
if (!net_device)
return -ENODEV;
+ /* We may race with netvsc_connect_vsp()/netvsc_init_buf() and get
+ * here before the negotiation with the host is finished and
+ * send_section_map may not be allocated yet.
+ */
+ if (!net_device->send_section_map)
+ return -EAGAIN;
+
out_channel = net_device->chn_table[q_idx];
packet->send_buf_index = NETVSC_INVALID_INDEX;
--
2.7.4
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