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rocker: fix neigh tbl index increment race

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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>
This commit is contained in:
Scott Feldman 2015-06-12 21:24:40 -07:00 committed by David S. Miller
parent a072031084
commit 4d81db4156
1 changed files with 2 additions and 2 deletions
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4
drivers/net/ethernet/rocker/rocker.c
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@ -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));