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b=dgyXsqH67FvyK+9N+RrmIuzBnPicK5E+nVD175qTBrUi/dZfe//hrorWytuL6wRpo g/WQLOOXYW9aoOx0MAwfabDfx6fXjkFvdm7PbfxgdHHnL9fSY4y2XNQ7fJZips1O8Q NBQBE0pdjLnBhjrbbOTs7Jlfa8pXiZwDxcbAiEq0= Date: Thu, 21 May 2026 15:31:30 -0700 From: Andrew Morton To: Alistair Popple Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, catalin.marinas@arm.com, will@kernel.org, david@kernel.org Subject: Re: [PATCH] arm64: mm: call pagetable dtor when freeing hot-removed page tables Message-Id: <20260521153130.d7d5cd060f7522f894252333@linux-foundation.org> In-Reply-To: <20260521032730.2104017-1-apopple@nvidia.com> References: <20260521032730.2104017-1-apopple@nvidia.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: yopos5wrn7m9iagu3ydgioksen1rir5g X-Rspamd-Queue-Id: 56A58100013 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1779402692-770131 X-HE-Meta: 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 93THqt9K CVpFbKSs/+RBdpSTcAcnpzkgWCdApaEUfKDM1uLIKBNMF2GOGjCGb0SSvJWrj+gDOg+MDo7vd/+//0b8OptM+be3kAQWF/5NP1EQ2yD8aIrEqQ26tccoKgEdPMtetULGsZ0FduRTRt3TTQO57SpePdunYwbt14Eszc2U4fNvoN3HZeF3dGdq10imlCvwJCPuGitfa0eDPF7lE+YTa7ktsiTqKR8C41uoznqBIZt9Wg8ybUr0vuMXjmwu/B5hGYzYX32f9cnOTw8lnbidJvH3Caj9Q/A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 21 May 2026 13:27:30 +1000 Alistair Popple wrote: > Since 5e8eb9aeeda3 ("arm64: mm: always call PTE/PMD ctor in > __create_pgd_mapping()") page-table allocation on ARM64 always > calls pagetable_{pte,pmd,pud,p4d}_ctor(). This sets the page_type > to PGTY_table, increments NR_PAGETABLE and possible allocates a PTL. > However the matching pagetable_dtor() calls were never added. > > With DEBUG_VM enabled on kernel versions prior to v6.17 without > 2dfcd1608f3a9 ("mm/page_alloc: let page freeing clear any set page > type") this leads to the following warning when freeing these pages due > to page->page_type sharing page->_mapcount: > > BUG: Bad page state in process ... pfn:284fbb > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x284fbb > flags: 0x17fffc000000000(node=0|zone=2|lastcpupid=0x1ffff) > page_type: f2(table) > page dumped because: nonzero mapcount > Call trace: > bad_page+0x13c/0x160 > __free_frozen_pages+0x6cc/0x860 > ___free_pages+0xf4/0x180 > free_pages+0x54/0x80 > free_hotplug_page_range.part.0+0x58/0x90 > free_empty_tables+0x438/0x500 > __remove_pgd_mapping.constprop.0+0x60/0xa8 > arch_remove_memory+0x48/0x80 > try_remove_memory+0x158/0x1d8 > offline_and_remove_memory+0x138/0x180 > > It can also lead to leaking the ptl allocation if ALLOC_SPLIT_PTLOCKS > is defined and incorrect NR_PAGETABLE stats. Fix this by calling > pagetable_dtor() in free_hotplug_pgtable_page() prior to freeing the > page to undo the effects of calling pagetable_*_ctor(). > > Fixes: 5e8eb9aeeda3 ("arm64: mm: always call PTE/PMD ctor in __create_pgd_mapping()") 6.16+, so I assume we want cc:stable here. > arch/arm64/mm/mmu.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 8e1d80a7033e..0c24fe650e95 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1422,6 +1422,7 @@ static void free_hotplug_page_range(struct page *page, size_t size, > > static void free_hotplug_pgtable_page(struct page *page) > { > + pagetable_dtor(page_ptdesc(page)); > free_hotplug_page_range(page, PAGE_SIZE, NULL); > } I'd of course prefer that arm maintainers handle this. But 5e8eb9aeeda3 came via myself so convention kinda-dictates that I get to fix it.