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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Selvin Xavier <selvin.xavier@broadcom.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.14 083/222] RDMA/bnxt_re: Fix recursive lock warning in debug kernel
Date:   Sun, 11 Nov 2018 14:23:00 -0800
Message-Id: <20181111221655.440985608@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Selvin Xavier <selvin.xavier@broadcom.com>

[ Upstream commit d455f29f6d76a5f94881ca1289aaa1e90617ff5d ]

Fix possible recursive lock warning. Its a false warning as the locks are
part of two differnt HW Queue data structure - cmdq and creq. Debug kernel
is throwing the following warning and stack trace.

[  783.914967] ============================================
[  783.914970] WARNING: possible recursive locking detected
[  783.914973] 4.19.0-rc2+ #33 Not tainted
[  783.914976] --------------------------------------------
[  783.914979] swapper/2/0 is trying to acquire lock:
[  783.914982] 000000002aa3949d (&(&hwq->lock)->rlock){..-.}, at: bnxt_qplib_service_creq+0x232/0x350 [bnxt_re]
[  783.914999]
but task is already holding lock:
[  783.915002] 00000000be73920d (&(&hwq->lock)->rlock){..-.}, at: bnxt_qplib_service_creq+0x2a/0x350 [bnxt_re]
[  783.915013]
other info that might help us debug this:
[  783.915016]  Possible unsafe locking scenario:

[  783.915019]        CPU0
[  783.915021]        ----
[  783.915034]   lock(&(&hwq->lock)->rlock);
[  783.915035]   lock(&(&hwq->lock)->rlock);
[  783.915037]
 *** DEADLOCK ***

[  783.915038]  May be due to missing lock nesting notation

[  783.915039] 1 lock held by swapper/2/0:
[  783.915040]  #0: 00000000be73920d (&(&hwq->lock)->rlock){..-.}, at: bnxt_qplib_service_creq+0x2a/0x350 [bnxt_re]
[  783.915044]
stack backtrace:
[  783.915046] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.19.0-rc2+ #33
[  783.915047] Hardware name: Dell Inc. PowerEdge R730/0599V5, BIOS 1.0.4 08/28/2014
[  783.915048] Call Trace:
[  783.915049]  <IRQ>
[  783.915054]  dump_stack+0x90/0xe3
[  783.915058]  __lock_acquire+0x106c/0x1080
[  783.915061]  ? sched_clock+0x5/0x10
[  783.915063]  lock_acquire+0xbd/0x1a0
[  783.915065]  ? bnxt_qplib_service_creq+0x232/0x350 [bnxt_re]
[  783.915069]  _raw_spin_lock_irqsave+0x4a/0x90
[  783.915071]  ? bnxt_qplib_service_creq+0x232/0x350 [bnxt_re]
[  783.915073]  bnxt_qplib_service_creq+0x232/0x350 [bnxt_re]
[  783.915078]  tasklet_action_common.isra.17+0x197/0x1b0
[  783.915081]  __do_softirq+0xcb/0x3a6
[  783.915084]  irq_exit+0xe9/0x100
[  783.915085]  do_IRQ+0x6a/0x120
[  783.915087]  common_interrupt+0xf/0xf
[  783.915088]  </IRQ>

Use nested notation for the spin_lock to avoid this warning.

Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/infiniband/hw/bnxt_re/qplib_rcfw.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/infiniband/hw/bnxt_re/qplib_rcfw.c
+++ b/drivers/infiniband/hw/bnxt_re/qplib_rcfw.c
@@ -311,8 +311,17 @@ static int bnxt_qplib_process_qp_event(s
 		bnxt_qplib_release_cq_locks(qp, &flags);
 		break;
 	default:
-		/* Command Response */
-		spin_lock_irqsave(&cmdq->lock, flags);
+		/*
+		 * Command Response
+		 * cmdq->lock needs to be acquired to synchronie
+		 * the command send and completion reaping. This function
+		 * is always called with creq->lock held. Using
+		 * the nested variant of spin_lock.
+		 *
+		 */
+
+		spin_lock_irqsave_nested(&cmdq->lock, flags,
+					 SINGLE_DEPTH_NESTING);
 		cookie = le16_to_cpu(qp_event->cookie);
 		mcookie = qp_event->cookie;
 		blocked = cookie & RCFW_CMD_IS_BLOCKING;