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;
 }