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 commitcad7f613c4
("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's4b10e7d562
("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>
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@ -1460,9 +1460,10 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
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if (__pmd_trans_huge_lock(pmd, vma) == 1) {
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pmd_t entry;
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entry = pmdp_get_and_clear(mm, addr, pmd);
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if (!prot_numa)
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if (!prot_numa) {
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entry = pmd_modify(entry, newprot);
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else {
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BUG_ON(pmd_write(entry));
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} else {
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struct page *page = pmd_page(*pmd);
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/* only check non-shared pages */
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@ -1471,7 +1472,6 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
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entry = pmd_mknuma(entry);
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}
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}
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BUG_ON(pmd_write(entry));
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set_pmd_at(mm, addr, pmd, entry);
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spin_unlock(&vma->vm_mm->page_table_lock);
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ret = 1;
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