From a19aa5c5fdda8b556ab238177ee27c5ef7873c94 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Fri, 11 Aug 2006 08:56:57 -0700 Subject: IB/mthca: Fix potential AB-BA deadlock with CQ locks When destroying a QP, mthca locks both the QP's send CQ and receive CQ. However, the following scenario is perfectly valid: QP_a: send_cq == CQ_x, recv_cq == CQ_y QP_b: send_cq == CQ_y, recv_cq == CQ_x The old mthca code simply locked send_cq and then recv_cq, which in this case could lead to an AB-BA deadlock if QP_a and QP_b were destroyed simultaneously. We can fix this by changing the locking code to lock the CQ with the lower CQ number first, which will create a consistent lock ordering. Also, the second CQ is locked with spin_lock_nested() to tell lockdep that we know what we're doing with the lock nesting. This bug was found by lockdep. Signed-off-by: Roland Dreier --- drivers/infiniband/hw/mthca/mthca_provider.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/infiniband/hw/mthca/mthca_provider.h') diff --git a/drivers/infiniband/hw/mthca/mthca_provider.h b/drivers/infiniband/hw/mthca/mthca_provider.h index 8de2887ba15..9a5bece3fa5 100644 --- a/drivers/infiniband/hw/mthca/mthca_provider.h +++ b/drivers/infiniband/hw/mthca/mthca_provider.h @@ -136,8 +136,8 @@ struct mthca_ah { * We have one global lock that protects dev->cq/qp_table. Each * struct mthca_cq/qp also has its own lock. An individual qp lock * may be taken inside of an individual cq lock. Both cqs attached to - * a qp may be locked, with the send cq locked first. No other - * nesting should be done. + * a qp may be locked, with the cq with the lower cqn locked first. + * No other nesting should be done. * * Each struct mthca_cq/qp also has an ref count, protected by the * corresponding table lock. The pointer from the cq/qp_table to the -- cgit v1.2.3