From 9f81036c54ed1f860d2807c5a6aa4f2b30c21204 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Mon, 21 May 2007 19:06:54 +0300 Subject: [PATCH] IB/cm: Improve local id allocation The IB CM uses an idr for local id allocations, with a running counter as start_id. This fails to generate distinct ids if 1. An id is constantly created and destroyed 2. A chunk of ids just beyond the current next_id value is occupied This in turn leads to an increased chance of connection request being mis-detected as a duplicate, sometimes for several retries, until next_id gets past the block of allocated ids. This has been observed in practice. As a fix, remember the last id allocated and start immediately above it. This also fixes a problem with the old code, where next_id might overflow and become negative. Signed-off-by: Michael S. Tsirkin Acked-by: Sean Hefty Signed-off-by: Roland Dreier --- drivers/infiniband/core/cm.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c index eff591deeb46..e840434a96d8 100644 --- a/drivers/infiniband/core/cm.c +++ b/drivers/infiniband/core/cm.c @@ -306,7 +306,9 @@ static int cm_alloc_id(struct cm_id_private *cm_id_priv) do { spin_lock_irqsave(&cm.lock, flags); ret = idr_get_new_above(&cm.local_id_table, cm_id_priv, - next_id++, &id); + next_id, &id); + if (!ret) + next_id = ((unsigned) id + 1) & MAX_ID_MASK; spin_unlock_irqrestore(&cm.lock, flags); } while( (ret == -EAGAIN) && idr_pre_get(&cm.local_id_table, GFP_KERNEL) ); -- 2.20.1