[PATCH 4.19 20/34] mm/thp: another PVMW_SYNC fix in page_vma_mapped_walk()

Greg Kroah-Hartman
2021-07-09T13:21:50Z

From: Hugh Dickins <hughd@google.com>

[ Upstream commit a7a69d8ba88d8dcee7ef00e91d413a4bd003a814 ]

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: Sasha Levin <sashal@kernel.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 b7a8009c1549..edca78609318 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -272,6 +272,10 @@ 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