Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Peter Xu <peterx@redhat.com>
To:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc:     David Hildenbrand <david@redhat.com>,
        Alistair Popple <apopple@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Johannes Weiner <hannes@cmpxchg.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>, peterx@redhat.com,
        Muhammad Usama Anjum <usama.anjum@collabora.com>,
        Hugh Dickins <hughd@google.com>,
        Mike Rapoport <rppt@kernel.org>
Subject: [PATCH 3/4] mm: Warn for unstable pmd in move_page_tables()
Date:   Fri,  2 Jun 2023 19:05:51 -0400
Message-Id: <20230602230552.350731-4-peterx@redhat.com>
In-Reply-To: <20230602230552.350731-1-peterx@redhat.com>
References: <20230602230552.350731-1-peterx@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

We already hold write mmap lock here, not possible to trigger unstable
pmd.  Make it a WARN_ON_ONCE instead.

Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/mremap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index da107f2c71bf..9303e4da4e7f 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -544,8 +544,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 					   old_pmd, new_pmd, need_rmap_locks))
 				continue;
 			split_huge_pmd(vma, old_pmd, old_addr);
-			if (pmd_trans_unstable(old_pmd))
-				continue;
+			/* We're with the mmap write lock, not possible to happen */
+			WARN_ON_ONCE(pmd_trans_unstable(old_pmd));
 		} else if (IS_ENABLED(CONFIG_HAVE_MOVE_PMD) &&
 			   extent == PMD_SIZE) {
 			/*
-- 
2.40.1