RDMA/irdma: 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.

Link: https://lore.kernel.org/r/20220418153322.42524-1-duoming@zju.edu.cn
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

diff --git a/drivers/infiniband/hw/irdma/cm.c b/drivers/infiniband/hw/irdma/cm.c
index dedb3b7edd8d6b43827b2bdb32cdade2f4906fdf..a98d962e5efb6601e7d543ce31ab1cf941d27b75 100644 (file)
--- a/drivers/infiniband/hw/irdma/cm.c
+++ b/drivers/infiniband/hw/irdma/cm.c
@@ -3246,15 +3246,10 @@ int irdma_setup_cm_core(struct irdma_device *iwdev, u8 rdma_ver)
  */
 void irdma_cleanup_cm_core(struct irdma_cm_core *cm_core)
 {
-       unsigned long flags;
-
        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);