> Subject: [PATCH V4 09/11] 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.
>
> What`s more, we add mod_timer() in order to guarantee the timer in
> irdma_schedule_cm_timer() and irdma_cm_timer_tick() could be executed.
>
> Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
> ---
> Changes in V4:
> - Add mod_timer() in order to guarantee the timer could be executed.
>
> drivers/infiniband/hw/irdma/cm.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/infiniband/hw/irdma/cm.c b/drivers/infiniband/hw/irdma/cm.c
> index dedb3b7edd8..e4117b978bf 100644
> --- a/drivers/infiniband/hw/irdma/cm.c
> +++ b/drivers/infiniband/hw/irdma/cm.c
> @@ -1184,6 +1184,8 @@ int irdma_schedule_cm_timer(struct irdma_cm_node
> *cm_node,
> if (!was_timer_set) {
> cm_core->tcp_timer.expires = new_send->timetosend;
> add_timer(&cm_core->tcp_timer);
> + } else {
> + mod_timer(&cm_core->tcp_timer, new_send->timetosend);
> }
There is no need to do a mod_timer. In the timer pending case, the handler will fire when the current armed timer expires.
The handler batch process connection nodes of interest. And this connection node is marked for processing.
> spin_unlock_irqrestore(&cm_core->ht_lock, flags);
>
> @@ -1367,6 +1369,8 @@ static void irdma_cm_timer_tick(struct timer_list *t)
> if (!timer_pending(&cm_core->tcp_timer)) {
> cm_core->tcp_timer.expires = nexttimeout;
> add_timer(&cm_core->tcp_timer);
> + } else {
> + mod_timer(&cm_core->tcp_timer, nexttimeout);
ditto. Please remove.
> }
> spin_unlock_irqrestore(&cm_core->ht_lock, flags);
> }
> @@ -3251,10 +3255,7 @@ 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);
This is fine.
Shiraz
