show_regs vs dump_stack in watchdog_timer_fn

Hello, Why the stack isn't always dumped in watchdog_timer_fn ([1])? Registers content is useful, but without a stack trace it's very hard to find the task which caused system softlockup. thanks, Daniel. [1] http://lxr.linux.no/linux+v2.6.39/kernel/watchdog.c#L292