From: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
commit 7aef4172c7957d7e65fc172be4c99becaef855d4 upstream.
With new refcounting we are going to see THP tail pages mapped with PTE.
Generic fast GUP rely on page_cache_get_speculative() to obtain
reference on page. page_cache_get_speculative() always fails on tail
pages, because ->_count on tail pages is always zero.
Let's handle tail pages in gup_pte_range().
New split_huge_page() will rely on migration entries to freeze page's
counts. Recheck PTE value after page_cache_get_speculative() on head
page should be enough to serialize against split.
Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Tested-by: Sasha Levin <sasha.le...@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
Acked-by: Jerome Marchand <jmarc...@redhat.com>
Acked-by: Vlastimil Babka <vba...@suse.cz>
Cc: Andrea Arcangeli <aarca...@redhat.com>
Cc: Hugh Dickins <hu...@google.com>
Cc: Dave Hansen <dave.han...@intel.com>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Rik van Riel <r...@redhat.com>
Cc: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
Cc: Steve Capper <steve.cap...@linaro.org>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Michal Hocko <mho...@suse.cz>
Cc: Christoph Lameter <c...@linux.com>
Cc: David Rientjes <rient...@google.com>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Ajay Kaher <aka...@vmware.com>
---
mm/gup.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 2cd3b31..45c544b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1070,7 +1070,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr,
unsigned long end,
* for an example see gup_get_pte in arch/x86/mm/gup.c
*/
pte_t pte = READ_ONCE(*ptep);
- struct page *page;
+ struct page *head, *page;
/*
* Similar to the PMD case below, NUMA hinting must take slow
@@ -1082,15 +1082,17 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr,
unsigned long end,
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
+ head = compound_head(page);
- if (!page_cache_get_speculative(page))
+ if (!page_cache_get_speculative(head))
goto pte_unmap;
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
- put_page(page);
+ put_page(head);
goto pte_unmap;
}
+ VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
(*nr)++;
--
2.7.4
