2022-04-20 01:33:46

by Duoming Zhou

Subject: [PATCH V6] RDMA/irdma: 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 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 <[email protected]>
---
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

2022-04-22 12:05:38

by Jason Gunthorpe

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

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 <[email protected]>
> ---
> 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