Converting ia64 kernel unwinder to lock free code

Converting ia64 kernel unwinder to lock free code

[Keith Owens]

MCA and INIT events are not irq safe, they can interrupt the kernel at
any point, including with spin_lock_irqsave() set.  We currently call
the ia64 kernel unwinder from MCA and INIT handlers, which has the
potential to deadlock or to return invalid results.  I want to convert
the kernel unwinder to be lock free, so it can be called from any
state.  That means no locks, and no calls to kernel sevices that might
deadlock, including printk and kmalloc.

Before I start on this task, are there any other plans for the kernel
unwinder code?  In the past davidm has hinted at replacing it with
libunwind.

Re: Converting ia64 kernel unwinder to lock free code

[David Mosberger]

>>>>> On Fri, 22 Oct 2004 14:25:55 +1000, Keith Owens <kaos@sgi.com> said:

  Keith> Before I start on this task, are there any other plans for
  Keith> the kernel unwinder code?  In the past davidm has hinted at
  Keith> replacing it with libunwind.

I definitely want to do that.  I'm not sure you can make it entirely
lock-free with caching enabled, but libunwind already works such that
if the lock is already taken, it bypasses the cache and hence doesn't
need to acquire the lock.

	--david