From: Michael S. Tsirkin Date: Mon, 21 May 2007 16:06:54 +0000 (+0300) Subject: IB/cm: Improve local id allocation X-Git-Tag: v2.6.22-rc3~108^2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f81036c54ed1f860d2807c5a6aa4f2b30c21204;p=linux-2.6 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 --- diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c index eff591deeb..e840434a96 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) );