On 3/20/15 6:47 PM, Linus Torvalds wrote:
Here's another data point: If I disable NUMA I don't see the problem.
Performance drops, but no NULL pointer splats which would have been panics.
So the NUMA case triggers the per-node "n->shared" logic, which
*should* be protected by "n->list_lock". Maybe there is some bug there
- but since that code seems to do ok on x86-64 (and apparently older
sparc too), I really would look at arch-specific issues first.
You raise a lot of valid questions and something to look into. But if
the root cause were such a fundamental issue (CPU memory ordering,
compiler bug, etc) why would it only occur on this one code path -- free
with SLAB and NUMA -- and so consistently?
Continuing to poke around, but open to any suggestions. I have enabled
every DEBUG I can find in the memory code and nothing is popping out. In
terms of races wouldn't all the DEBUG checks affect timing? Yet, I am
still seeing the same stack traces due to the same root cause.
David
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