* [PATCH V5] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()
@ 2022-04-17 13:14 Duoming Zhou
2022-04-18 14:57 ` Saleem, Shiraz
0 siblings, 1 reply; 3+ messages in thread
From: Duoming Zhou @ 2022-04-17 13:14 UTC (permalink / raw)
To: linux-kernel
Cc: mustafa.ismail, shiraz.saleem, jgg, leon, linux-rdma, 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 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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* RE: [PATCH V5] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()
2022-04-17 13:14 [PATCH V5] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core() Duoming Zhou
@ 2022-04-18 14:57 ` Saleem, Shiraz
2022-04-18 15:41 ` duoming
0 siblings, 1 reply; 3+ messages in thread
From: Saleem, Shiraz @ 2022-04-18 14:57 UTC (permalink / raw)
To: Duoming Zhou, linux-kernel; +Cc: Ismail, Mustafa, jgg, leon, linux-rdma
> 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 <duoming@zju.edu.cn>
> ---
> 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 <shiraz.saleem@intel.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: RE: [PATCH V5] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core()
2022-04-18 14:57 ` Saleem, Shiraz
@ 2022-04-18 15:41 ` duoming
0 siblings, 0 replies; 3+ messages in thread
From: duoming @ 2022-04-18 15:41 UTC (permalink / raw)
To: Saleem, Shiraz; +Cc: linux-kernel, Ismail, Mustafa, jgg, leon, linux-rdma
Hello,
On Mon, 18 Apr 2022 14:57:06 +0000 Saleem, Shiraz 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 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.
I think the deadlock is possible, because the timer is a delay mechanism that could execute at any time, although all CM nodes are culled.
> 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: "
I sent "[PATCH V6] RDMA/irdma: Fix deadlock in irdma_cleanup_cm_core()" just now.
Best regards,
Duoming Zhou
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-04-17 13:14 [PATCH V5] drivers: infiniband: hw: Fix deadlock in irdma_cleanup_cm_core() Duoming Zhou
2022-04-18 14:57 ` Saleem, Shiraz
2022-04-18 15:41 ` duoming
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