[PATCH V6] RDMA/irdma: Fix deadlock in irdma_cleanup_cm_core()

[PATCH V6] RDMA/irdma: 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 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.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in V6:
  - Change subject line prefixed with "RDMA/irdma: ".

 drivers/infiniband/hw/irdma/cm.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/infiniband/hw/irdma/cm.c b/drivers/infiniband/hw/irdma/cm.c
index dedb3b7edd8..4b6b1065f85 100644
--- a/drivers/infiniband/hw/irdma/cm.c
+++ b/drivers/infiniband/hw/irdma/cm.c
@@ -3251,10 +3251,7 @@ void irdma_cleanup_cm_core(struct irdma_cm_core *cm_core)
 	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);
-- 
2.17.1

Re: [PATCH V6] RDMA/irdma: Fix deadlock in irdma_cleanup_cm_core()

[Jason Gunthorpe]

On Mon, Apr 18, 2022 at 11:33:22PM +0800, Duoming Zhou wrote:
> 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.
> 
> Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> ---
> Changes in V6:
>   - Change subject line prefixed with "RDMA/irdma: ".
> 
>  drivers/infiniband/hw/irdma/cm.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)

I fixed the compile warning.

Applied to for-rc, thanks

Jason