From 3f08842098e842c51e3b97d0dcdebf810b32558e Mon Sep 17 00:00:00 2001

From: Shijie Luo <luoshijie1@huawei.com>

Date: Sun, 1 Nov 2020 17:07:40 -0800

Subject: [PATCH] mm: mempolicy: fix potential pte_unmap_unlock pte error

Git-commit: 3f08842098e842c51e3b97d0dcdebf810b32558e

Patch-mainline: v5.10-rc3

References: bsc#1185906

When flags in queue_pages_pte_range don't have MPOL_MF_MOVE or

MPOL_MF_MOVE_ALL bits, code breaks and passing origin pte - 1 to

pte_unmap_unlock seems like not a good idea.

queue_pages_pte_range can run in MPOL_MF_MOVE_ALL mode which doesn't

migrate misplaced pages but returns with EIO when encountering such a

page.  Since commit a7f40cfe3b7a ("mm: mempolicy: make mbind() return

-EIO when MPOL_MF_STRICT is specified") and early break on the first pte

in the range results in pte_unmap_unlock on an underflow pte.  This can

lead to lockups later on when somebody tries to lock the pte resp.

page_table_lock again..

Fixes: a7f40cfe3b7a ("mm: mempolicy: make mbind() return -EIO when MPOL_MF_STRICT is specified")

Signed-off-by: Shijie Luo <luoshijie1@huawei.com>

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Reviewed-by: Oscar Salvador <osalvador@suse.de>

Acked-by: Michal Hocko <mhocko@suse.com>

Cc: Miaohe Lin <linmiaohe@huawei.com>

Cc: Feilong Lin <linfeilong@huawei.com>

Cc: Shijie Luo <luoshijie1@huawei.com>

Cc: <stable@vger.kernel.org>

Link: https://lkml.kernel.org/r/20201019074853.50856-1-luoshijie1@huawei.com

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

---

 mm/mempolicy.c |    8 ++++----

 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/mm/mempolicy.c

+++ b/mm/mempolicy.c

@@ -492,7 +492,7 @@ static int queue_pages_pte_range(pmd_t *

 	struct queue_pages *qp = walk->private;

 	unsigned long flags = qp->flags;

 	int nid, ret;

-	pte_t *pte;

+	pte_t *pte, *mapped_pte;

 	spinlock_t *ptl;

 	if (pmd_trans_huge(*pmd)) {

@@ -543,7 +543,7 @@ static int queue_pages_pte_range(pmd_t *

 	if (pmd_trans_unstable(pmd))

 		return 0;

 retry:

-	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);

+	mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);

 	for (; addr != end; pte++, addr += PAGE_SIZE) {

 		if (!pte_present(*pte))

 			continue;

@@ -576,7 +576,7 @@ retry:

 			if (ret) {

 				if (flags & MPOL_MF_STRICT)

 					return -EIO;

-				pte = pte_offset_map_lock(walk->mm, pmd,

+				mapped_pte = pte_offset_map_lock(walk->mm, pmd,

 						addr, &ptl);

 				continue;

 			}

@@ -590,7 +590,7 @@ retry:

 		} else

 			break;

 	}

-	pte_unmap_unlock(pte - 1, ptl);

+	pte_unmap_unlock(mapped_pte, ptl);

 	cond_resched();

 	return addr != end ? -EIO : 0;

 }