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Date: Sat, 21 Mar 2015 11:45:07 -0600 From: David Ahern <david.ahern@...cle.com> To: Linus Torvalds <torvalds@...ux-foundation.org> CC: linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: 4.0.0-rc4: panic in free_block 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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