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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id o9-20020a0dcc09000000b0056d2fce4e09sm379759ywd.42.2023.06.20.00.45.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jun 2023 00:45:31 -0700 (PDT) Date: Tue, 20 Jun 2023 00:45:26 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Andrew Morton cc: Gerald Schaefer , Vasily Gorbik , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David S. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Jann Horn , Vishal Moola , Vlastimil Babka , linux-arm-kernel@lists.infradead.org, sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 04/12] powerpc: assert_pte_locked() use pte_offset_map_nolock() In-Reply-To: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com> Message-ID: <7ae6836b-b612-23f1-63e0-babda6e96e2c@google.com> References: <54cb04f-3762-987f-8294-91dafd8ebfb0@google.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 --- 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 l= ong addr) p4d_t *p4d; pud_t *pud; pmd_t *pmd; + pte_t *pte; + spinlock_t *ptl; =20 if (mm =3D=3D &init_mm) return; @@ -321,16 +323,10 @@ void assert_pte_locked(struct mm_struct *mm, unsigned= long addr) pud =3D pud_offset(p4d, addr); BUG_ON(pud_none(*pud)); pmd =3D 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 =3D pte_offset_map_nolock(mm, pmd, addr, &ptl); + BUG_ON(!pte); + assert_spin_locked(ptl); + pte_unmap(pte); } #endif /* CONFIG_DEBUG_VM */ =20 --=20 2.35.3