Re: [PATCH] mm: fix kernel BUG at huge_memory.c:1474!

From: Linus Torvalds
Date: Sun Dec 16 2012 - 22:00:22 EST

On Sun, Dec 16, 2012 at 6:56 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> Andrea's autonuma-benchmark numa01 hits kernel BUG at huge_memory.c:1474!
> in change_huge_pmd called from change_protection from change_prot_numa
> from task_numa_work.
> That BUG, introduced in the huge zero page commit cad7f613c4d0 ("thp:
> change_huge_pmd(): make sure we don't try to make a page writable")
> was trying to verify that newprot never adds write permission to an
> anonymous huge page; but Automatic NUMA Balancing's 4b10e7d562c9 ("mm:
> mempolicy: Implement change_prot_numa() in terms of change_protection()")
> adds a new prot_numa path into change_huge_pmd(), which makes no use of
> the newprot provided, and may retain the write bit in the pmd.

Ok. I did wonder about that particular conflict, but it looked like
neither case was writable, so I resolved it wrongly, and it worked for
me, but then I don't have any numa setups, nor do I even enable it..


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