[PATCH 5.4 221/367] ntb: Fix calculation ntb_transport_tx_free_entry()

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5.4-stable review patch.  If anyone has any objections, please let me know.


From: Dave Jiang <dave.jiang@xxxxxxxxx>

commit 5a7693e6bbf19b22fd6c1d2c4b7beb0a03969e2c upstream.

ntb_transport_tx_free_entry() never returns 0 with the current
calculation. If head == tail, then it would return qp->tx_max_entry.
Change compare to tail >= head and when they are equal, a 0 would be

Fixes: e74bfeedad08 ("NTB: Add flow control to the ntb_netdev")
Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Signed-off-by: renlonglong <ren.longlong@xxxxxxx>
Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
Signed-off-by: Jon Mason <jdmason@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
 drivers/ntb/ntb_transport.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -2431,7 +2431,7 @@ unsigned int ntb_transport_tx_free_entry
 	unsigned int head = qp->tx_index;
 	unsigned int tail = qp->remote_rx_info->entry;
-	return tail > head ? tail - head : qp->tx_max_entry + tail - head;
+	return tail >= head ? tail - head : qp->tx_max_entry + tail - head;

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