Commit a4f1de17 authored Dec 16, 2012 by Hugh Dickins Committed by Linus Torvalds Dec 16, 2012

mm: fix kernel BUG at huge_memory.c:1474!

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 cad7f613 ("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 4b10e7d5 ("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.

Just move the BUG_ON(pmd_write(entry)) up into the !prot_numa block.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2dfea380

mm/huge_memory.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -1460,9 +1460,10 @@ int change_huge_pmd(struct vm_area_struct vma, pmd_t pmd,
		if (__pmd_trans_huge_lock(pmd, vma) == 1) {
		pmd_t entry;
		entry = pmdp_get_and_clear(mm, addr, pmd);
		if (!prot_numa)
		if (!prot_numa) {
		entry = pmd_modify(entry, newprot);
		else {
		BUG_ON(pmd_write(entry));
		} else {
		struct page page = pmd_page(pmd);

		/* only check non-shared pages */
		@@ -1471,7 +1472,6 @@ int change_huge_pmd(struct vm_area_struct vma, pmd_t pmd,
		entry = pmd_mknuma(entry);
		}
		}
		BUG_ON(pmd_write(entry));
		set_pmd_at(mm, addr, pmd, entry);
		spin_unlock(&vma->vm_mm->page_table_lock);
		ret = 1;

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