rocker: fix neigh tbl index increment race

rocker->neigh_tbl_next_index is used to generate unique indices for neigh
entries programmed into the device.  The way new indices were generated was
racy with the new prepare-commit transaction model.  A simple fix here
removes the race.  The race was with two processes getting the same index,
one process using prepare-commit, the other not:

Proc A					Proc B

PREPARE phase
get neigh_tbl_next_index

					NONE phase
					get neigh_tbl_next_index
					neigh_tbl_next_index++

COMMIT phase
neigh_tbl_next_index++

Both A and B got the same index.  The fix is to store and increment
neigh_tbl_next_index in the PREPARE (or NONE) phase and use value in COMMIT
phase:

Proc A					Proc B

PREPARE phase
get neigh_tbl_next_index
neigh_tbl_next_index++

					NONE phase
					get neigh_tbl_next_index
					neigh_tbl_next_index++

COMMIT phase
// use value stashed in PREPARE phase

Reported-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/rocker/rocker.c b/drivers/net/ethernet/rocker/rocker.c
index c6a6e3c36d9073c5852b5f38fec9a59f31cc3cb0..a9d15590743eb59b955c7c6ce39ea9c8bb9a77bc 100644 (file)
--- a/drivers/net/ethernet/rocker/rocker.c
+++ b/drivers/net/ethernet/rocker/rocker.c
@@ -2901,10 +2901,10 @@ static void _rocker_neigh_add(struct rocker *rocker,
                              enum switchdev_trans trans,
                              struct rocker_neigh_tbl_entry *entry)
 {
-       entry->index = rocker->neigh_tbl_next_index;
+       if (trans != SWITCHDEV_TRANS_COMMIT)
+               entry->index = rocker->neigh_tbl_next_index++;
        if (trans == SWITCHDEV_TRANS_PREPARE)
                return;
-       rocker->neigh_tbl_next_index++;
        entry->ref_count++;
        hash_add(rocker->neigh_tbl, &entry->entry,
                 be32_to_cpu(entry->ip_addr));