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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 <rolandd@cisco.com>
This commit is contained in:
Roland Dreier 2006-08-11 08:56:57 -07:00
parent e54b82d739
commit a19aa5c5fd
2 changed files with 32 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/infiniband/hw/mthca/mthca_provider.h
View File

@ -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

42
drivers/infiniband/hw/mthca/mthca_qp.c
View File

@ -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));