linux-kernel - [PATCH v3 04/13] powerpc: assert_pte_locked() use pte_offset_map

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Date:   Tue, 11 Jul 2023 21:34:25 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Yang Shi <shy828301@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Peter Xu <peterx@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Steven Price <steven.price@....com>,
        SeongJae Park <sj@...nel.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Huang Ying <ying.huang@...el.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Zack Rusin <zackr@...are.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Minchan Kim <minchan@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Song Liu <song@...nel.org>,
        Thomas Hellstrom <thomas.hellstrom@...ux.intel.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Jann Horn <jannh@...gle.com>,
        Vishal Moola <vishal.moola@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
        linux-arm-kernel@...ts.infradead.org, sparclinux@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v3 04/13] powerpc: assert_pte_locked() use
 pte_offset_map_nolock()

Instead of pte_lockptr(), use the recently added pte_offset_map_nolock()
in assert_pte_locked().  BUG if pte_offset_map_nolock() fails: this is
stricter than the previous implementation, which skipped when pmd_none()
(with a comment on khugepaged collapse transitions): but wouldn't we want
to know, if an assert_pte_locked() caller can be racing such transitions?

This mod might cause new crashes: which either expose my ignorance, or
indicate issues to be fixed, or limit the usage of assert_pte_locked().

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
 arch/powerpc/mm/pgtable.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index cb2dcdb18f8e..16b061af86d7 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -311,6 +311,8 @@ void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
 	p4d_t *p4d;
 	pud_t *pud;
 	pmd_t *pmd;
+	pte_t *pte;
+	spinlock_t *ptl;
 
 	if (mm == &init_mm)
 		return;
@@ -321,16 +323,10 @@ void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
 	pud = pud_offset(p4d, addr);
 	BUG_ON(pud_none(*pud));
 	pmd = pmd_offset(pud, addr);
-	/*
-	 * khugepaged to collapse normal pages to hugepage, first set
-	 * pmd to none to force page fault/gup to take mmap_lock. After
-	 * pmd is set to none, we do a pte_clear which does this assertion
-	 * so if we find pmd none, return.
-	 */
-	if (pmd_none(*pmd))
-		return;
-	BUG_ON(!pmd_present(*pmd));
-	assert_spin_locked(pte_lockptr(mm, pmd));
+	pte = pte_offset_map_nolock(mm, pmd, addr, &ptl);
+	BUG_ON(!pte);
+	assert_spin_locked(ptl);
+	pte_unmap(pte);
 }
 #endif /* CONFIG_DEBUG_VM */
 
-- 
2.35.3