linux-kernel - [PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap

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Date:	Wed, 15 Jun 2016 23:06:10 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Yang Shi <yang.shi@...aro.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Ning Qu <quning@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Ebru Akagunduz <ebru.akagunduz@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap_sem re-acquired

Vlastimil noted[1] that pmd can be no longer valid after we drop
mmap_sem. We need recheck it once mmap_sem taken again.

[1] http://lkml.kernel.org/r/12918dcd-a695-c6f4-e06f-69141c5f357f@suse.cz

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/huge_memory.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d7ccc8558187..0efdad975659 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2437,6 +2437,9 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 			/* vma is no longer available, don't continue to swapin */
 			if (hugepage_vma_revalidate(mm, address))
 				return false;
+			/* check if the pmd is still valid */
+			if (mm_find_pmd(mm, address) != pmd)
+				return false;
 		}
 		if (ret & VM_FAULT_ERROR) {
 			trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
@@ -2522,6 +2525,9 @@ static void collapse_huge_page(struct mm_struct *mm,
 	result = hugepage_vma_revalidate(mm, address);
 	if (result)
 		goto out;
+	/* check if the pmd is still valid */
+	if (mm_find_pmd(mm, address) != pmd)
+		goto out;
 
 	anon_vma_lock_write(vma->anon_vma);
 
-- 
2.8.1