linux-kernel - [PATCH AUTOSEL 5.15 02/19] RDMA/irdma: Fix deadlock in irdma_cleanup_cm

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Message-Id: <20220510154429.153677-2-sashal@kernel.org>
Date:   Tue, 10 May 2022 11:44:12 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Duoming Zhou <duoming@....edu.cn>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Sasha Levin <sashal@...nel.org>, mustafa.ismail@...el.com,
        linux-rdma@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 02/19] RDMA/irdma: Fix deadlock in irdma_cleanup_cm_core()

From: Duoming Zhou <duoming@....edu.cn>

[ Upstream commit 679ab61bf5f5f519377d812afb4fb93634782c74 ]

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 removes the check of timer_pending() in
irdma_cleanup_cm_core(), because the del_timer_sync() function will just
return directly if there isn't a pending timer. As a result, the lock is
redundant, because there is no resource it could protect.

Link: https://lore.kernel.org/r/20220418153322.42524-1-duoming@zju.edu.cn
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
Reviewed-by: Shiraz Saleem <shiraz.saleem@...el.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/infiniband/hw/irdma/cm.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/infiniband/hw/irdma/cm.c b/drivers/infiniband/hw/irdma/cm.c
index 6dea0a49d171..41703c7ebca5 100644
--- a/drivers/infiniband/hw/irdma/cm.c
+++ b/drivers/infiniband/hw/irdma/cm.c
@@ -3244,15 +3244,10 @@ enum irdma_status_code irdma_setup_cm_core(struct irdma_device *iwdev,
  */
 void irdma_cleanup_cm_core(struct irdma_cm_core *cm_core)
 {
-	unsigned long flags;
-
 	if (!cm_core)
 		return;
 
-	spin_lock_irqsave(&cm_core->ht_lock, flags);
-	if (timer_pending(&cm_core->tcp_timer))
-		del_timer_sync(&cm_core->tcp_timer);
-	spin_unlock_irqrestore(&cm_core->ht_lock, flags);
+	del_timer_sync(&cm_core->tcp_timer);
 
 	destroy_workqueue(cm_core->event_wq);
 	cm_core->dev->ws_reset(&cm_core->iwdev->vsi);
-- 
2.35.1