[dpdk-dev] [PATCH v2 1/4] bus/vmbus: fix race in sub channel creation

[Stephen Hemminger <stephen@networkplumber.org>]

When using multiple queues, there was a race with the kernel
in setting up the second channel. This regression is due to a kernel change
which does not allow accessing sysfs files for Hyper-V channels that are not opened.

The fix is simple, just move the logic to detect not ready
sub channels earlier in the existing loop.

Fixes: 831dba47bd36 ("bus/vmbus: add Hyper-V virtual bus support")
Reported-by:Mohammed Gamal <mgamal@redhat.com>
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
---
 drivers/bus/vmbus/linux/vmbus_uio.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/bus/vmbus/linux/vmbus_uio.c b/drivers/bus/vmbus/linux/vmbus_uio.c
index 12e97e3a420a..38df4d724ed5 100644
--- a/drivers/bus/vmbus/linux/vmbus_uio.c
+++ b/drivers/bus/vmbus/linux/vmbus_uio.c
@@ -357,6 +357,12 @@ int vmbus_uio_get_subchan(struct vmbus_channel *primary,
 			continue;
 		}
 
+		if (!vmbus_isnew_subchannel(primary, relid))
+			continue;	/* Already know about you */
+
+		if (!vmbus_uio_ring_present(dev, relid))
+			continue;	/* Ring may not be ready yet */
+
 		snprintf(subchan_path, sizeof(subchan_path), "%s/%lu",
 			 chan_path, relid);
 		err = vmbus_uio_sysfs_read(subchan_path, "subchannel_id",
@@ -370,12 +376,6 @@ int vmbus_uio_get_subchan(struct vmbus_channel *primary,
 		if (subid == 0)
 			continue;	/* skip primary channel */
 
-		if (!vmbus_isnew_subchannel(primary, relid))
-			continue;
-
-		if (!vmbus_uio_ring_present(dev, relid))
-			continue;	/* Ring may not be ready yet */
-
 		err = vmbus_uio_sysfs_read(subchan_path, "monitor_id",
 					   &monid, UINT8_MAX);
 		if (err) {
-- 
2.19.2