linux-kernel - [PATCH 4.4 034/105] thp: reduce indentation level in change_huge

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Message-Id: <20171215092307.726849819@linuxfoundation.org>
Date:   Fri, 15 Dec 2017 10:44:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jack Wang <jinpu.wang@...fitbricks.com>
Subject: [PATCH 4.4 034/105] thp: reduce indentation level in change_huge_pmd()

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

commit 0a85e51d37645e9ce57e5e1a30859e07810ed07c upstream.

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: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Hillf Danton <hillf.zj@...baba-inc.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[jwang: adjust context for 4.4 kernel]
Signed-off-by: Jack Wang <jinpu.wang@...fitbricks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/huge_memory.c |   54 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 28 insertions(+), 26 deletions(-)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1566,35 +1566,37 @@ int change_huge_pmd(struct vm_area_struc
 {
 	struct mm_struct *mm = vma->vm_mm;
 	spinlock_t *ptl;
+	pmd_t entry;
+	bool preserve_write;
+
 	int ret = 0;
 
-	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
-		pmd_t entry;
-		bool preserve_write = prot_numa && pmd_write(*pmd);
-		ret = 1;
-
-		/*
-		 * Avoid trapping faults against the zero page. The read-only
-		 * 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 || !pmd_protnone(*pmd)) {
-			entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
-			entry = pmd_modify(entry, newprot);
-			if (preserve_write)
-				entry = pmd_mkwrite(entry);
-			ret = HPAGE_PMD_NR;
-			set_pmd_at(mm, addr, pmd, entry);
-			BUG_ON(!preserve_write && pmd_write(entry));
-		}
-		spin_unlock(ptl);
-	}
+	if (__pmd_trans_huge_lock(pmd, vma, &ptl) != 1)
+		return 0;
+
+	preserve_write = prot_numa && pmd_write(*pmd);
+	ret = 1;
+
+	/*
+	 * Avoid trapping faults against the zero page. The read-only
+	 * 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))
+		goto unlock;
+
+	if (prot_numa && pmd_protnone(*pmd))
+		goto unlock;
 
+	entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
+	entry = pmd_modify(entry, newprot);
+	if (preserve_write)
+		entry = pmd_mkwrite(entry);
+	ret = HPAGE_PMD_NR;
+	set_pmd_at(mm, addr, pmd, entry);
+	BUG_ON(!preserve_write && pmd_write(entry));
+unlock:
+	spin_unlock(ptl);
 	return ret;
 }