2022-04-18 05:16:13

by Duoming Zhou

Subject: [PATCH V5] 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 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 V5:
- Remove mod_timer() in irdma_schedule_cm_timer and irdma_cm_timer_tick.

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

2022-04-20 10:30:40

by Shiraz Saleem

Subject: RE: [PATCH V5] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()

> Subject: [PATCH V5] 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 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 V5:
> - Remove mod_timer() in irdma_schedule_cm_timer and irdma_cm_timer_tick.
>
> 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);
> --

I am not sure the deadlock is possible practically since all CM nodes should be culled by the time we get to irdma_cleanup_cm_core.

However, timer_pending check and locks are redundant and should be removed.

The subject line for patches to our driver are typically prefixed with "RDMA/irdma: "

Reviewed-by: Shiraz Saleem <[email protected]>