linux-kernel - [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm

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Date:   Thu,  7 Apr 2022 14:37:12 +0800
From:   Duoming Zhou <duoming@....edu.cn>
To:     linux-kernel@...r.kernel.org
Cc:     chris@...kel.net, jcmvbkbc@...il.com, mustafa.ismail@...el.com,
        shiraz.saleem@...el.com, jgg@...pe.ca, wg@...ndegger.com,
        mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, jes@...ined-monkey.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        alexander.deucher@....com, linux-xtensa@...ux-xtensa.org,
        linux-rdma@...r.kernel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-hippi@...site.dk,
        linux-staging@...ts.linux.dev, linux-serial@...r.kernel.org,
        linux-usb@...r.kernel.org, Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH 09/11] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()

There is a deadlock in irdma_cleanup_cm_core(), which is shown
below:

   (Thread 1)              |      (Thread 2)
                           | irdma_schedule_cm_timer()
irdma_cleanup_cm_core()    |  add_timer()
 spin_lock_irqsave() //(1) |  (wait a time)
 ...                       | irdma_cm_timer_tick()
 del_timer_sync()          |  spin_lock_irqsave() //(2)
 (wait timer to stop)      |  ...

We hold cm_core->ht_lock in position (1) of thread 1 and
use del_timer_sync() to wait timer to stop, but timer handler
also need cm_core->ht_lock in position (2) of thread 2.
As a result, irdma_cleanup_cm_core() will block forever.

This patch extracts del_timer_sync() from the protection of
spin_lock_irqsave(), which could let timer handler to obtain
the needed lock.

Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
 drivers/infiniband/hw/irdma/cm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/irdma/cm.c b/drivers/infiniband/hw/irdma/cm.c
index dedb3b7edd8..019dd8bfe08 100644
--- a/drivers/infiniband/hw/irdma/cm.c
+++ b/drivers/infiniband/hw/irdma/cm.c
@@ -3252,8 +3252,11 @@ void irdma_cleanup_cm_core(struct irdma_cm_core *cm_core)
 		return;
 
 	spin_lock_irqsave(&cm_core->ht_lock, flags);
-	if (timer_pending(&cm_core->tcp_timer))
+	if (timer_pending(&cm_core->tcp_timer)) {
+		spin_unlock_irqrestore(&cm_core->ht_lock, flags);
 		del_timer_sync(&cm_core->tcp_timer);
+		spin_lock_irqsave(&cm_core->ht_lock, flags);
+	}
 	spin_unlock_irqrestore(&cm_core->ht_lock, flags);
 
 	destroy_workqueue(cm_core->event_wq);
-- 
2.17.1