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Commit 0a85e51d authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
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thp: reduce indentation level in change_huge_pmd() 

Patch series "thp: fix few MADV_DONTNEED races"

For MADV_DONTNEED to work properly with huge pages, it's critical to not
clear pmd intermittently unless you hold down_write(mmap_sem).

Otherwise MADV_DONTNEED can miss the THP which can lead to userspace
breakage.

See example of such race in commit message of patch 2/4.

All these races are found by code inspection.  I haven't seen them
triggered.  I don't think it's worth to apply them to stable@.

This patch (of 4):

Restructure code in preparation for a fix.

Link: http://lkml.kernel.org/r/20170302151034.27829-2-kirill.shutemov@linux.intel.com


Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 76e32a2a

mm/huge_memory.c

+26 −26
Original line number Diff line number Diff line
@@ -1724,12 +1724,15 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, 
{

	struct mm_struct *mm = vma->vm_mm;

	spinlock_t *ptl;

	int ret = 0;

	pmd_t entry;

	bool preserve_write;

	int ret;



	ptl = __pmd_trans_huge_lock(pmd, vma);

	if (ptl) {

		pmd_t entry;

		bool preserve_write = prot_numa && pmd_write(*pmd);

	if (!ptl)

		return 0;



	preserve_write = prot_numa && pmd_write(*pmd);

	ret = 1;



	/*
@@ -1737,24 +1740,21 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, 
	 * data is likely to be read-cached on the local CPU and

	 * local/remote hits to the zero page are not interesting.

	 */

		if (prot_numa && is_huge_zero_pmd(*pmd)) {

			spin_unlock(ptl);

			return ret;

		}

	if (prot_numa && is_huge_zero_pmd(*pmd))

		goto unlock;



	if (prot_numa && pmd_protnone(*pmd))

		goto unlock;



		if (!prot_numa || !pmd_protnone(*pmd)) {

	entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);

	entry = pmd_modify(entry, newprot);

	if (preserve_write)

		entry = pmd_mk_savedwrite(entry);

	ret = HPAGE_PMD_NR;

	set_pmd_at(mm, addr, pmd, entry);

			BUG_ON(vma_is_anonymous(vma) && !preserve_write &&

					pmd_write(entry));

		}

	BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));

unlock:

	spin_unlock(ptl);

	}



	return ret;

}