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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Hugh Dickins <hughd@google.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Wang Yugui <wangyugui@e16-tech.com>,
        Alistair Popple <apopple@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>,
        Peter Xu <peterx@redhat.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Will Deacon <will@kernel.org>, Yang Shi <shy828301@gmail.com>,
        Zi Yan <ziy@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: [PATCH 5.4 65/71] mm/thp: another PVMW_SYNC fix in page_vma_mapped_walk()
Date:   Mon, 28 Jun 2021 10:29:58 -0400
Message-Id: <20210628143004.32596-66-sashal@kernel.org>
In-Reply-To: <20210628143004.32596-1-sashal@kernel.org>
References: <20210628143004.32596-1-sashal@kernel.org>
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From: Hugh Dickins <hughd@google.com>

Aha! Shouldn't that quick scan over pte_none()s make sure that it holds
ptlock in the PVMW_SYNC case? That too might have been responsible for
BUGs or WARNs in split_huge_page_to_list() or its unmap_page(), though
I've never seen any.

Link: https://lkml.kernel.org/r/1bdf384c-8137-a149-2a1e-475a4791c3c@google.com
Link: https://lore.kernel.org/linux-mm/20210412180659.B9E3.409509F4@e16-tech.com/
Fixes: ace71a19cec5 ("mm: introduce page_vma_mapped_walk()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Wang Yugui <wangyugui@e16-tech.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/page_vma_mapped.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 0e8f54683709..029f5598251c 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -271,6 +271,10 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 				goto restart;
 			}
 			pvmw->pte++;
+			if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
+				pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
+				spin_lock(pvmw->ptl);
+			}
 		} while (pte_none(*pvmw->pte));
 
 		if (!pvmw->ptl) {
-- 
2.30.2