On Mon, Jul 03, 2017 at 03:49:42PM -0700, Linus Torvalds wrote: > On Mon, Jul 3, 2017 at 3:30 PM, Paul E. McKenney > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > That certainly is one interesting function, isn't it? I wonder what > > happens if you replace the raw_spin_is_locked() calls with an > > unlock under a trylock check? ;-) > > Deadlock due to interrupts again? Unless I am missing something subtle, the kgdb_cpu_enter() function in question has a local_irq_save() over the "interesting" portion of its workings, so interrupt-handler self-deadlock should not happen. > Didn't your spin_unlock_wait() patches teach you anything? Checking > state is fundamentally different from taking the lock. Even a trylock. That was an embarrassing bug, no two ways about it. :-/ > I guess you could try with the irqsave versions. But no, we're not doing that. Again, no need in this case. But I agree with Will's assessment of this function... The raw_spin_is_locked() looks to be asking if -any- CPU holds the dbg_slave_lock, and the answer could of course change immediately on return from raw_spin_is_locked(). Perhaps the theory is that if other CPU holds the lock, this CPU is supposed to be subjected to kgdb_roundup_cpus(). Except that the CPU that held dbg_slave_lock might be just about to release that lock. Odd. Seems like there should be a get_online_cpus() somewhere, but maybe that constraint is to be manually enforced. Thanx, Paul
