[PATCH 09/11] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()

[Duoming Zhou]

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@xxxxxxxxxx>
---
 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