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

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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 cad7f613c4 ("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 4b10e7d562 ("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>
This commit is contained in:
Hugh Dickins 2012-12-16 18:56:58 -08:00 committed by Linus Torvalds
parent 2dfea3803d
commit a4f1de1766
1 changed files with 3 additions and 3 deletions
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6
mm/huge_memory.c
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@ -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;