From a19aa5c5fdda8b556ab238177ee27c5ef7873c94 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Fri, 11 Aug 2006 08:56:57 -0700 Subject: [PATCH] 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 +- drivers/infiniband/hw/mthca/mthca_qp.c | 42 ++++++++++++++------ 2 files changed, 32 insertions(+), 14 deletions(-) diff --git a/drivers/infiniband/hw/mthca/mthca_provider.h b/drivers/infiniband/hw/mthca/mthca_provider.h index 8de2887ba15c..9a5bece3fa5c 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 diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c index 157b4f8ac407..2e8f6f36e0a5 100644 --- a/drivers/infiniband/hw/mthca/mthca_qp.c +++ b/drivers/infiniband/hw/mthca/mthca_qp.c @@ -1263,6 +1263,32 @@ int mthca_alloc_qp(struct mthca_dev *dev, return 0; } +static void mthca_lock_cqs(struct mthca_cq *send_cq, struct mthca_cq *recv_cq) +{ + if (send_cq == recv_cq) + spin_lock_irq(&send_cq->lock); + else if (send_cq->cqn < recv_cq->cqn) { + spin_lock_irq(&send_cq->lock); + spin_lock_nested(&recv_cq->lock, SINGLE_DEPTH_NESTING); + } else { + spin_lock_irq(&recv_cq->lock); + spin_lock_nested(&send_cq->lock, SINGLE_DEPTH_NESTING); + } +} + +static void mthca_unlock_cqs(struct mthca_cq *send_cq, struct mthca_cq *recv_cq) +{ + if (send_cq == recv_cq) + spin_unlock_irq(&send_cq->lock); + else if (send_cq->cqn < recv_cq->cqn) { + spin_unlock(&recv_cq->lock); + spin_unlock_irq(&send_cq->lock); + } else { + spin_unlock(&send_cq->lock); + spin_unlock_irq(&recv_cq->lock); + } +} + int mthca_alloc_sqp(struct mthca_dev *dev, struct mthca_pd *pd, struct mthca_cq *send_cq, @@ -1315,17 +1341,13 @@ int mthca_alloc_sqp(struct mthca_dev *dev, * Lock CQs here, so that CQ polling code can do QP lookup * without taking a lock. */ - spin_lock_irq(&send_cq->lock); - if (send_cq != recv_cq) - spin_lock(&recv_cq->lock); + mthca_lock_cqs(send_cq, recv_cq); spin_lock(&dev->qp_table.lock); mthca_array_clear(&dev->qp_table.qp, mqpn); spin_unlock(&dev->qp_table.lock); - if (send_cq != recv_cq) - spin_unlock(&recv_cq->lock); - spin_unlock_irq(&send_cq->lock); + mthca_unlock_cqs(send_cq, recv_cq); err_out: dma_free_coherent(&dev->pdev->dev, sqp->header_buf_size, @@ -1359,9 +1381,7 @@ void mthca_free_qp(struct mthca_dev *dev, * Lock CQs here, so that CQ polling code can do QP lookup * without taking a lock. */ - spin_lock_irq(&send_cq->lock); - if (send_cq != recv_cq) - spin_lock(&recv_cq->lock); + mthca_lock_cqs(send_cq, recv_cq); spin_lock(&dev->qp_table.lock); mthca_array_clear(&dev->qp_table.qp, @@ -1369,9 +1389,7 @@ void mthca_free_qp(struct mthca_dev *dev, --qp->refcount; spin_unlock(&dev->qp_table.lock); - if (send_cq != recv_cq) - spin_unlock(&recv_cq->lock); - spin_unlock_irq(&send_cq->lock); + mthca_unlock_cqs(send_cq, recv_cq); wait_event(qp->wait, !get_qp_refcount(dev, qp));