[PATCH 1/2] nvmet-rdma: Avoid that nvmet_rdma_release_queue_work() triggers a lockdep complaint

[bvanassche@acm.org (Bart Van Assche)]

Call flush_work() instead of flush_workqueue(). That is sufficient to
suppress the following lockdep complaint (see also commit 87915adc3f0a
("workqueue: re-add lockdep dependencies for flushing")):

======================================================
WARNING: possible circular locking dependency detected
4.19.0-dbg+ #1 Not tainted
------------------------------------------------------
kworker/u12:0/7 is trying to acquire lock:
00000000c03a91d1 (&id_priv->handler_mutex){+.+.}, at: rdma_destroy_id+0x6f/0x440 [rdma_cm]

but task is already holding lock:
(work_completion)(&queue->release_work)){+.+.}, at: process_one_work+0x3c9/0x9f0
which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:
-> #3 ((work_completion)(&queue->release_work)){+.+.}:
       process_one_work+0x447/0x9f0
       worker_thread+0x63/0x5a0
       kthread+0x1cf/0x1f0
       ret_from_fork+0x24/0x30
-> #2 ((wq_completion)"nvmet-rdma-delete-wq"){+.+.}:
       flush_workqueue+0xf3/0x970
       nvmet_rdma_cm_handler+0x1320/0x170f [nvmet_rdma]
       cma_ib_req_handler+0x72f/0xf90 [rdma_cm]
       cm_process_work+0x2e/0x110 [ib_cm]
       cm_work_handler+0x431e/0x50ba [ib_cm]
       process_one_work+0x481/0x9f0
       worker_thread+0x63/0x5a0
       kthread+0x1cf/0x1f0
       ret_from_fork+0x24/0x30
-> #1 (&id_priv->handler_mutex/1){+.+.}:
       __mutex_lock+0xfe/0xbe0
       mutex_lock_nested+0x1b/0x20
       cma_ib_req_handler+0x6aa/0xf90 [rdma_cm]
       cm_process_work+0x2e/0x110 [ib_cm]
       cm_work_handler+0x431e/0x50ba [ib_cm]
       process_one_work+0x481/0x9f0
       worker_thread+0x63/0x5a0
       kthread+0x1cf/0x1f0
       ret_from_fork+0x24/0x30
-> #0 (&id_priv->handler_mutex){+.+.}:
       lock_acquire+0xc5/0x200
       __mutex_lock+0xfe/0xbe0
       mutex_lock_nested+0x1b/0x20
       rdma_destroy_id+0x6f/0x440 [rdma_cm]
       nvmet_rdma_release_queue_work+0x8e/0x1b0 [nvmet_rdma]
       process_one_work+0x481/0x9f0
       worker_thread+0x63/0x5a0
       kthread+0x1cf/0x1f0
       ret_from_fork+0x24/0x30
other info that might help us debug this:
Chain exists of:
  &id_priv->handler_mutex --> (wq_completion)"nvmet-rdma-delete-wq" --> (work_completion)(&queue->release_work)

Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&queue->release_work));
                               lock((wq_completion)"nvmet-rdma-delete-wq");
                               lock((work_completion)(&queue->release_work));
  lock(&id_priv->handler_mutex);

 *** DEADLOCK ***

2 locks held by kworker/u12:0/7:
 #0: 00000000272134f2 ((wq_completion)"nvmet-rdma-delete-wq"){+.+.}, at: process_one_work+0x3c9/0x9f0
 #1: 0000000090531fcd ((work_completion)(&queue->release_work)){+.+.}, at: process_one_work+0x3c9/0x9f0

               stack backtrace:
CPU: 1 PID: 7 Comm: kworker/u12:0 Not tainted 4.19.0-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Workqueue: nvmet-rdma-delete-wq nvmet_rdma_release_queue_work [nvmet_rdma]
Call Trace:
 dump_stack+0x86/0xc5
 print_circular_bug.isra.32+0x20a/0x218
 __lock_acquire+0x1c68/0x1cf0
 lock_acquire+0xc5/0x200
 __mutex_lock+0xfe/0xbe0
 mutex_lock_nested+0x1b/0x20
 rdma_destroy_id+0x6f/0x440 [rdma_cm]
 nvmet_rdma_release_queue_work+0x8e/0x1b0 [nvmet_rdma]
 process_one_work+0x481/0x9f0
 worker_thread+0x63/0x5a0
 kthread+0x1cf/0x1f0
 ret_from_fork+0x24/0x30

Cc: Sagi Grimberg <sagi at grimberg.me>
Cc: Johannes Berg <johannes.berg at intel.com>
Signed-off-by: Bart Van Assche <bvanassche at acm.org>
---
 drivers/nvme/target/rdma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/target/rdma.c b/drivers/nvme/target/rdma.c
index bd265aceb90c..b3ee64fd66c5 100644
--- a/drivers/nvme/target/rdma.c
+++ b/drivers/nvme/target/rdma.c
@@ -1268,7 +1268,7 @@ static int nvmet_rdma_queue_connect(struct rdma_cm_id *cm_id,
 
 	if (queue->host_qid == 0) {
 		/* Let inflight controller teardown complete */
-		flush_workqueue(nvmet_rdma_delete_wq);
+		flush_work(&queue->release_work);
 	}
 
 	ret = nvmet_rdma_cm_accept(cm_id, queue, &event->param.conn);
-- 
2.19.1.568.g152ad8e336-goog