On Thu, Apr 07, 2022 at 02:37:12PM +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 extracts del_timer_sync() from the protection of
> spin_lock_irqsave(), which could let timer handler to obtain
> the needed lock.
>
> Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> ---
> drivers/infiniband/hw/irdma/cm.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/hw/irdma/cm.c b/drivers/infiniband/hw/irdma/cm.c
> index dedb3b7edd8..019dd8bfe08 100644
> --- a/drivers/infiniband/hw/irdma/cm.c
> +++ b/drivers/infiniband/hw/irdma/cm.c
> @@ -3252,8 +3252,11 @@ void irdma_cleanup_cm_core(struct irdma_cm_core *cm_core)
> return;
>
> spin_lock_irqsave(&cm_core->ht_lock, flags);
> - if (timer_pending(&cm_core->tcp_timer))
> + if (timer_pending(&cm_core->tcp_timer)) {
> + spin_unlock_irqrestore(&cm_core->ht_lock, flags);
> del_timer_sync(&cm_core->tcp_timer);
> + spin_lock_irqsave(&cm_core->ht_lock, flags);
> + }
> spin_unlock_irqrestore(&cm_core->ht_lock, flags);
This lock doesn't seem to be protecting anything. Also do we need to
check timer_pending()? I think the del_timer_sync() function will just
return directly if there isn't a pending lock?
regards,
dan carpenter
