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authorMike Marciniszyn <mike.marciniszyn@intel.com>2013-02-07 20:47:51 +0000
committerRoland Dreier <roland@purestorage.com>2013-02-14 17:04:18 -0800
commitbcc9b67a5b65ec2e1ec5371226a729ec1b380860 (patch)
tree23edbc2c2964ee07d5c96c4ab3f5e697ad248fa6 /drivers
parent836dc9e3fbbab0c30aa6e664417225f5c1fb1c39 (diff)
IB/qib: Fix QP locate/remove race
remove_qp() can execute concurrently with a qib_lookup_qpn() on another CPU, which in of itself, is ok, given the RCU locking. The issue is that remove_qp() NULLs out the qp->next field so that a qib_lookup_qpn() might fail to find a qp if it occurs after the one that is being deleted. This is a momentary issue and subsequent qib_lookup_qpn() calls would find the qp's since the search restarts from the bucket head. At scale, the issue might causes dropped packets and unnecessary retransmissions. The fix just deletes the qp->next NULL assignment to prevent the remove_qp() from hiding qp's from qib_lookup_qpn(). Reviewed-by: Dean Luick <dean.luick@intel.com> Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com> Signed-off-by: Roland Dreier <roland@purestorage.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/infiniband/hw/qib/qib_qp.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/infiniband/hw/qib/qib_qp.c b/drivers/infiniband/hw/qib/qib_qp.c
index 35275099cafd..a6a2cc2ba260 100644
--- a/drivers/infiniband/hw/qib/qib_qp.c
+++ b/drivers/infiniband/hw/qib/qib_qp.c
@@ -268,8 +268,9 @@ static void remove_qp(struct qib_ibdev *dev, struct qib_qp *qp)
qpp = &q->next)
if (q == qp) {
atomic_dec(&qp->refcount);
- *qpp = qp->next;
- rcu_assign_pointer(qp->next, NULL);
+ rcu_assign_pointer(*qpp,
+ rcu_dereference_protected(qp->next,
+ lockdep_is_held(&dev->qpt_lock)));
break;
}
}