Re: [PATCH v2 14/14] mm/page-flags: remove PG_private
From: sashiko-bot@kernel.org
Date: 2026-09-01 00:16:15
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [High] Removal of PG_private safety check causes leaked filesystem private data to go undetected. -- commit 9b27f18c6460a8f0a47a836096a558c0ddbb879d Author: Zi Yan [off-list ref] Subject: mm/page-flags: remove PG_private This patch removes the PG_private flag and repurposes its space as __PG_folio. It replaces the flag checks with checking if folio->private != NULL to determine if a folio carries private data. It also updates relevant documentation to reflect these changes.
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diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index ae2ebaed6d4d9..02e67307ffff4 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h
[ ... ]
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@@ -1169,7 +1170,7 @@ static __always_inline void __ClearPageAnonExclusive(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 | \ 1UL << PG_writeback | 1UL << PG_reserved | \ 1UL << PG_active | \ 1UL << PG_unevictable | __PG_MLOCKED | LRU_GEN_MASK)
[Severity: High]
Does removing PG_private from this mask cause leaked filesystem private data
to go undetected?
By removing the PG_private check without adding a replacement check for
folio->private != NULL on the head page, the memory allocator's validation
routines no longer catch this leak.
Instead, when a buggy filesystem or subsystem frees a page with a non-NULL
private field, free_pages_prepare() in mm/page_alloc.c will unconditionally
zero it without warning:
mm/page_alloc.c:free_pages_prepare() {
...
page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP;
page->private = 0;
...
}
Could this silently erase the leaked private data (such as buffer heads) and
mask the underlying memory leak?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260831-remove-pg_private-v2-0-3668159cd9e8@nvidia.com?part=14