Re: 4KSTACKS + DEBUG_STACKOVERFLOW harmful

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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
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