linux-kernel - Re: [PATCH V6] RDMA/irdma: Fix deadlock in irdma_cleanup_cm

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Date:   Tue, 19 Apr 2022 13:13:51 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Duoming Zhou <duoming@....edu.cn>
Cc:     linux-kernel@...r.kernel.org, shiraz.saleem@...el.com,
        mustafa.ismail@...el.com, leon@...nel.org,
        linux-rdma@...r.kernel.org
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 <duoming@....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