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authorRoland Dreier <rolandd@cisco.com>2006-08-11 08:56:57 -0700
committerRoland Dreier <rolandd@cisco.com>2006-08-11 08:56:57 -0700
commita19aa5c5fdda8b556ab238177ee27c5ef7873c94 (patch)
tree6c770c8fbbe3270bf1416c3edd8894d214e62657 /drivers/infiniband/hw/mthca/mthca_provider.h
parente54b82d739d4a2ef992976c8c0692cdf89286420 (diff)
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>
Diffstat (limited to 'drivers/infiniband/hw/mthca/mthca_provider.h')
-rw-r--r--drivers/infiniband/hw/mthca/mthca_provider.h4
1 files changed, 2 insertions, 2 deletions
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