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Subject[PATCH 3.16 009/136] RDMA/iwcm: Fix a lock inversion issue
3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Bart Van Assche <bvanassche@acm.org>

commit b66f31efbdad95ec274345721d99d1d835e6de01 upstream.

This patch fixes the lock inversion complaint:

============================================
WARNING: possible recursive locking detected
5.3.0-rc7-dbg+ #1 Not tainted
--------------------------------------------
kworker/u16:6/171 is trying to acquire lock:
00000000035c6e6c (&id_priv->handler_mutex){+.+.}, at: rdma_destroy_id+0x78/0x4a0 [rdma_cm]

but task is already holding lock:
00000000bc7c307d (&id_priv->handler_mutex){+.+.}, at: iw_conn_req_handler+0x151/0x680 [rdma_cm]

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&id_priv->handler_mutex);
lock(&id_priv->handler_mutex);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by kworker/u16:6/171:
#0: 00000000e2eaa773 ((wq_completion)iw_cm_wq){+.+.}, at: process_one_work+0x472/0xac0
#1: 000000001efd357b ((work_completion)(&work->work)#3){+.+.}, at: process_one_work+0x476/0xac0
#2: 00000000bc7c307d (&id_priv->handler_mutex){+.+.}, at: iw_conn_req_handler+0x151/0x680 [rdma_cm]

stack backtrace:
CPU: 3 PID: 171 Comm: kworker/u16:6 Not tainted 5.3.0-rc7-dbg+ #1
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
Workqueue: iw_cm_wq cm_work_handler [iw_cm]
Call Trace:
dump_stack+0x8a/0xd6
__lock_acquire.cold+0xe1/0x24d
lock_acquire+0x106/0x240
__mutex_lock+0x12e/0xcb0
mutex_lock_nested+0x1f/0x30
rdma_destroy_id+0x78/0x4a0 [rdma_cm]
iw_conn_req_handler+0x5c9/0x680 [rdma_cm]
cm_work_handler+0xe62/0x1100 [iw_cm]
process_one_work+0x56d/0xac0
worker_thread+0x7a/0x5d0
kthread+0x1bc/0x210
ret_from_fork+0x24/0x30

This is not a bug as there are actually two lock classes here.

Link: https://lore.kernel.org/r/20190930231707.48259-3-bvanassche@acm.org
Fixes: de910bd92137 ("RDMA/cma: Simplify locking needed for serialization of callbacks")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/infiniband/core/cma.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -1549,9 +1549,10 @@ static int iw_conn_req_handler(struct iw
conn_id->cm_id.iw = NULL;
cma_exch(conn_id, RDMA_CM_DESTROYING);
mutex_unlock(&conn_id->handler_mutex);
+ mutex_unlock(&listen_id->handler_mutex);
cma_deref_id(conn_id);
rdma_destroy_id(&conn_id->id);
- goto out;
+ return ret;
}

mutex_unlock(&conn_id->handler_mutex);
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