The following crash was observed:

  Unable to handle kernel NULL pointer dereference at 0000000000000158
  Internal error: Oops: 96000004 [#1] SMP
  pc : resend_irqs+0x68/0xb0
  lr : resend_irqs+0x64/0xb0
  ...
  Call trace:
   resend_irqs+0x68/0xb0
   tasklet_action_common.isra.6+0x84/0x138
   tasklet_action+0x2c/0x38
   __do_softirq+0x120/0x324
   run_ksoftirqd+0x44/0x60
   smpboot_thread_fn+0x1ac/0x1e8
   kthread+0x134/0x138
   ret_from_fork+0x10/0x18

The reason for this is that the interrupt resend mechanism happens in soft
interrupt context, which is a asynchronous mechanism versus other
operations on interrupts. free_irq() does not take resend handling into
account. Thus, the irq descriptor might be already freed before the resend
tasklet is executed. resend_irqs() does not check the return value of the
interrupt descriptor lookup and derefences the return value
unconditionally.

  1):
  __setup_irq
    irq_startup
      check_irq_resend  /...