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Sashiko AI review found 2 potential issu= e(s) to consider: > - [High] mm: silent loss of memory leak detection for page->private on he= ad pages at free time > - [Medium] mm: removal of KPF_PRIVATE from /proc/kpageflags breaks usersp= ace ABI > -- > > commit 11221906706fcf50f2069964f35b9ce234eeabe6 > Author: Zi Yan > > mm/page-flags: check page/folio->private instead of PG_private > > After the changes of the prior commits, page/folio->private !=3D NULL is = now > equivalent to checking PG_private. Stop checking PG_private on pages and > folios and use page/folio->private instead, except swapcache and hugetlb. > >> diff --git a/fs/proc/page.c b/fs/proc/page.c >> index 260772b20bd99..f90e1030825e9 100644 >> --- a/fs/proc/page.c >> +++ b/fs/proc/page.c >> @@ -232,7 +232,6 @@ u64 stable_page_flags(const struct page *page) >> >> u |=3D kpf_copy_bit(k, KPF_RESERVED, PG_reserved); >> u |=3D kpf_copy_bit(k, KPF_OWNER_2, PG_owner_2); >> - u |=3D kpf_copy_bit(k, KPF_PRIVATE, PG_private); > > [Severity: Medium] > Does removing the KPF_PRIVATE bit from stable_page_flags() break the > userspace ABI? > > Any userspace tool or script relying on this bit to identify private page= s > will silently fail to detect them. Could this be preserved by computing i= t > via folio_has_attached_private(folio) instead? No. It is intended and userspace tools need to cope with it. > > [ ... ] > >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index 7080a6a1a79e7..6d839f50bdcb7 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h > > [ ... ] > >> @@ -1169,7 +1191,7 @@ 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: High] > Does removing PG_private from PAGE_FLAGS_CHECK_AT_FREE mask memory leaks > of filesystem private data for head pages? > > Any buggy filesystem or driver that frees a page with an attached > page->private structure will silently leak it without a kernel warning. > In mm/page_alloc.c, __free_pages_prepare() unconditionally executes: > > page->private =3D 0; > > Since PG_private was removed from PAGE_FLAGS_CHECK_AT_FREE, there is no > longer a check that page->private was zero before this assignment, meanin= g > the leaked pointer is zeroed out for the head page without any validation > or warning. > > The equivalent explicit check for tail pages was preserved, indicating th= e > loss of the head page check might be an unintended oversight when removin= g > the flag. 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/ > > [ ... ] > >> diff --git a/tools/mm/page-types.c b/tools/mm/page-types.c >> index 7fc5a8be5997f..47e4781c5fc38 100644 >> --- a/tools/mm/page-types.c >> +++ b/tools/mm/page-types.c > > [ ... ] > >> @@ -131,7 +130,6 @@ static const char * const page_flag_names[] =3D { >> [KPF_RESERVED] =3D "r:reserved", >> [KPF_MLOCKED] =3D "m:mlocked", >> [KPF_OWNER_2] =3D "d:owner_2", >> - [KPF_PRIVATE] =3D "P:private", >> [KPF_PRIVATE_2] =3D "p:private_2", > > [Severity: Medium] > Does removing the flag name from page_flag_names in page-types.c break > parsing tools relying on the P:private designation? Will send a separate patch to fix page-type.c > > --=20 > Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260920-remove-p= g_private-v5-0-bb68b6a21869@nvidia.com?part=3D10 Best Regards, Yan, Zi