RDMA/bnxt_re: Avoid Hard lockup during error CQE processing

Hitting the following hardlockup due to a race condition in
error CQE processing.

[26146.879798] bnxt_en 0000:04:00.0: QPLIB: FP: CQ Processed Req
[26146.886346] bnxt_en 0000:04:00.0: QPLIB: wr_id[1251] = 0x0 with status 0xa
[26156.350935] NMI watchdog: Watchdog detected hard LOCKUP on cpu 4
[26156.357470] Modules linked in: nfsd auth_rpcgss nfs_acl lockd grace
[26156.447957] CPU: 4 PID: 3413 Comm: kworker/4:1H Kdump: loaded
[26156.457994] Hardware name: Dell Inc. PowerEdge R430/0CN7X8,
[26156.466390] Workqueue: ib-comp-wq ib_cq_poll_work [ib_core]
[26156.472639] Call Trace:
[26156.475379]  <NMI>  [<ffffffff98d0d722>] dump_stack+0x19/0x1b
[26156.481833]  [<ffffffff9873f775>] watchdog_overflow_callback+0x135/0x140
[26156.489341]  [<ffffffff9877f237>] __perf_event_overflow+0x57/0x100
[26156.496256]  [<ffffffff98787c24>] perf_event_overflow+0x14/0x20
[26156.502887]  [<ffffffff9860a580>] intel_pmu_handle_irq+0x220/0x510
[26156.509813]  [<ffffffff98d16031>] perf_event_nmi_handler+0x31/0x50
[26156.516738]  [<ffffffff98d1790c>] nmi_handle.isra.0+0x8c/0x150
[26156.523273]  [<ffffffff98d17be8>] do_nmi+0x218/0x460
[26156.528834]  [<ffffffff98d16d79>] end_repeat_nmi+0x1e/0x7e
[26156.534980]  [<ffffffff987089c0>] ? native_queued_spin_lock_slowpath+0x1d0/0x200
[26156.543268]  [<ffffffff987089c0>] ? native_queued_spin_lock_slowpath+0x1d0/0x200
[26156.551556]  [<ffffffff987089c0>] ? native_queued_spin_lock_slowpath+0x1d0/0x200
[26156.559842]  <EOE>  [<ffffffff98d083e4>] queued_spin_lock_slowpath+0xb/0xf
[26156.567555]  [<ffffffff98d15690>] _raw_spin_lock+0x20/0x30
[26156.573696]  [<ffffffffc08381a1>] bnxt_qplib_lock_buddy_cq+0x31/0x40 [bnxt_re]
[26156.581789]  [<ffffffffc083bbaa>] bnxt_qplib_poll_cq+0x43a/0xf10 [bnxt_re]
[26156.589493]  [<ffffffffc083239b>] bnxt_re_poll_cq+0x9b/0x760 [bnxt_re]

The issue happens if RQ poll_cq or SQ poll_cq or Async error event tries to
put the error QP in flush list. Since SQ and RQ of each error qp are added
to two different flush list, we need to protect it using locks of
corresponding CQs. Difference in order of acquiring the lock in
SQ poll_cq and RQ poll_cq can cause a hard lockup.

Revisits the locking strategy and removes the usage of qplib_cq.hwq.lock.
Instead of this lock, introduces qplib_cq.flush_lock to handle
addition/deletion of QPs in flush list. Also, always invoke the flush_lock
in order (SQ CQ lock first and then RQ CQ lock) to avoid any potential
deadlock.

Other than the poll_cq context, the movement of QP to/from flush list can
be done in modify_qp context or from an async error event from HW.
Synchronize these operations using the bnxt_re verbs layer CQ locks.
To achieve this, adds a call back to the HW abstraction layer(qplib) to
bnxt_re ib_verbs layer in case of async error event. Also, removes the
buddy cq functions as it is no longer required.

Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/drivers/infiniband/hw/bnxt_re/ib_verbs.c b/drivers/infiniband/hw/bnxt_re/ib_verbs.c
index 755f1ccd82bb..0dd75f449872 100644
--- a/drivers/infiniband/hw/bnxt_re/ib_verbs.c
+++ b/drivers/infiniband/hw/bnxt_re/ib_verbs.c
@@ -785,7 +785,7 @@ int bnxt_re_query_ah(struct ib_ah *ib_ah, struct rdma_ah_attr *ah_attr)
 	return 0;
 }
 
-static unsigned long bnxt_re_lock_cqs(struct bnxt_re_qp *qp)
+unsigned long bnxt_re_lock_cqs(struct bnxt_re_qp *qp)
 	__acquires(&qp->scq->cq_lock) __acquires(&qp->rcq->cq_lock)
 {
 	unsigned long flags;
@@ -799,8 +799,8 @@ static unsigned long bnxt_re_lock_cqs(struct bnxt_re_qp *qp)
 	return flags;
 }
 
-static void bnxt_re_unlock_cqs(struct bnxt_re_qp *qp,
-			       unsigned long flags)
+void bnxt_re_unlock_cqs(struct bnxt_re_qp *qp,
+			unsigned long flags)
 	__releases(&qp->scq->cq_lock) __releases(&qp->rcq->cq_lock)
 {
 	if (qp->rcq != qp->scq)
@@ -1606,6 +1606,7 @@ int bnxt_re_modify_qp(struct ib_qp *ib_qp, struct ib_qp_attr *qp_attr,
 	int status;
 	union ib_gid sgid;
 	struct ib_gid_attr sgid_attr;
+	unsigned int flags;
 	u8 nw_type;
 
 	qp->qplib_qp.modify_flags = 0;
@@ -1634,14 +1635,18 @@ int bnxt_re_modify_qp(struct ib_qp *ib_qp, struct ib_qp_attr *qp_attr,
 			dev_dbg(rdev_to_dev(rdev),
 				"Move QP = %p to flush list\n",
 				qp);
+			flags = bnxt_re_lock_cqs(qp);
 			bnxt_qplib_add_flush_qp(&qp->qplib_qp);
+			bnxt_re_unlock_cqs(qp, flags);
 		}
 		if (!qp->sumem &&
 		    qp->qplib_qp.state == CMDQ_MODIFY_QP_NEW_STATE_RESET) {
 			dev_dbg(rdev_to_dev(rdev),
 				"Move QP = %p out of flush list\n",
 				qp);
+			flags = bnxt_re_lock_cqs(qp);
 			bnxt_qplib_clean_qp(&qp->qplib_qp);
+			bnxt_re_unlock_cqs(qp, flags);
 		}
 	}
 	if (qp_attr_mask & IB_QP_EN_SQD_ASYNC_NOTIFY) {