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Commit bcc9b67a authored by Mike Marciniszyn's avatar Mike Marciniszyn Committed by Roland Dreier
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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: default avatarDean Luick <dean.luick@intel.com>
Signed-off-by: default avatarMike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: default avatarRoland Dreier <roland@purestorage.com>
parent 836dc9e3

drivers/infiniband/hw/qib/qib_qp.c

+3 −2
Original line number Diff line number Diff line
@@ -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;

			}

	}