Re: 4KSTACKS + DEBUG_STACKOVERFLOW harmful

Kyle Moffett
2007-08-29T23:55:22Z

On Aug 29, 2007, at 19:01:57, Eric Sandeen wrote:
> Jesper Juhl wrote:
>> A first step could be to allocate those two char arrays with
>> kmalloc() instead of on the stack, but then I guess that dump_stack
>> () gets called from places where we may not really want to be
>> calling kmalloc(). I guess we could allocate the buffers earlier
>> (like at boot time) and store pointers somewhere where dump stack
>> can get to them later when it needs them.
>
> Yep, I thought about something like that... and I assume you'd need
> a bit of locking around them too.

How about turning off preemption and using a per-CPU buffer?
Alternatively you could turn off IRQs, poke a per-CPU value to clue
in any incoming NMIs, and switch to a separate stack. I suppose if
you wanted it to work with all of 16 bytes of stack left on both
thread and IRQ stacks, you could have separate per-CPU NMI stacks;
the stack-dump would be poking a special per-CPU value and sending
ourselves an NMI.

There are probably a half dozen other variants on ways to run
screaming to the CPU saying "It hurts mommy!" and get a new stack in
which we can play for a while.

Cheers,
Kyle Moffett