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Howlett" , Matthew Wilcox , Suren Baghdasaryan , Nico Pache , Johannes Weiner , Gregory Price , Kairui Song , David Hildenbrand , Michal Hocko , Alistair Popple , Baolin Wang , Vlastimil Babka , Lance Yang , Lorenzo Stoakes , Andrew Morton , Barry Song , Ryan Roberts , Qi Zheng , Dev Jain , Ying Huang , Usama Arif , Mike Rapoport , Jan Kara , Jonathan Corbet , Pasha Tatashin , linux-mm@kvack.org, Mathieu Desnoyers , kexec@lists.infradead.org, Masami Hiramatsu , Pratyush Yadav , linux-doc@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Baoquan He , linux-kernel@vger.kernel.org, Dave Young , Steven Rostedt , Shuah Khan , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v5 17/17] mm/page-flags: remove PG_private Date: Mon, 21 Sep 2026 11:36:27 -0400 X-Mailer: MailMate (3.0r7032) Message-ID: In-Reply-To: <20260921025520.628971F000FF@smtp.kernel.org> References: <20260920-remove-pg_private-v5-0-bb68b6a21869@nvidia.com> <20260920-remove-pg_private-v5-17-bb68b6a21869@nvidia.com> <20260921025520.628971F000FF@smtp.kernel.org> Content-Type: text/plain; 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Sashiko AI review found 1 potential issu= e(s) to consider: > - [Medium] mm: silent memory leak masking due to PG_private removal > -- > > commit aee12ed3446e69cb6eee57384ca09e768dab36dd > Author: Zi Yan > > mm/page-flags: remove PG_private > > This commit removes the PG_private page flag and replaces its usage with > checking if folio->private !=3D NULL. The space left by PG_private is > reserved as PG_folio for future use. > >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index 7080a6a1a79e7..b0ddc652e76cc 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h > [ ... ] >> @@ -1169,7 +1175,7 @@ static __always_inline void __ClearPageAnonExclusi= ve(struct page *page) >> */ >> #define PAGE_FLAGS_CHECK_AT_FREE \ >> (1UL << PG_lru | 1UL << PG_locked | \ >> - 1UL << PG_private | 1UL << PG_private_2 | \ >> + 1UL << PG_private_2 | \ > > [Severity: Medium] > Since PG_private is removed from PAGE_FLAGS_CHECK_AT_FREE, does this bypa= ss > the safety check that ensures a page doesn't have uncleared private data? > > Looking at __free_pages_prepare() in mm/page_alloc.c: > > page_cpupid_reset_last(page); > page->flags.f &=3D ~PAGE_FLAGS_CHECK_AT_PREP; > page->private =3D 0; > reset_page_owner(page, order); > > The head page's private field is silently zeroed here without any prior > verification that it was NULL. Previously, free_page_is_bad() would catch > and report leaked data via a bad_page() warning using > PAGE_FLAGS_CHECK_AT_FREE. > > Now, if a buggy filesystem fails to detach and free folio->private data > before freeing the page, will this result in silent memory leaks? Answer copied from RFC: After the conversion, folio/page should have an elevated refcount whenever ->private is set. That would help detect leaked private data. I tried to enforce ->private needs to be NULL at page free time[1], but that might cause trouble for certain use cases. [1] https://lore.kernel.org/all/20260223032641.1859381-1-ziy@nvidia.com/ > >> 1UL << PG_writeback | 1UL << PG_reserved | \ >> 1UL << PG_active | \ >> 1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK) > > --=20 > Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260920-remove-p= g_private-v5-0-bb68b6a21869@nvidia.com?part=3D17 Best Regards, Yan, Zi