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Fri, 06 Feb 2026 10:25:21 -0800 (PST) MIME-Version: 1.0 References: <20260206174017.128673-1-mikhail.v.gavrilov@gmail.com> <3BB6BA1D-3756-4FC6-B00D-79DF49D75C51@nvidia.com> In-Reply-To: <3BB6BA1D-3756-4FC6-B00D-79DF49D75C51@nvidia.com> From: Kairui Song Date: Sat, 7 Feb 2026 02:24:45 +0800 X-Gm-Features: AZwV_Qj9ArkpXSETCK1paJ36vy4F_CRQBBxAfzS6Lq5DExmenMFaALVelzse_U8 Message-ID: Subject: Re: [PATCH] mm/page_alloc: clear page->private in split_page() for tail pages To: Zi Yan Cc: Mikhail Gavrilov , linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@suse.cz, chrisl@kernel.org, hughd@google.com, stable@vger.kernel.org, David Hildenbrand , surenb@google.com, Matthew Wilcox , mhocko@suse.com, hannes@cmpxchg.org, jackmanb@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Stat-Signature: 1w61iu64fib77q9zecxqdxprjm9mahmg X-Rspamd-Queue-Id: 5C5E7160004 X-Rspam-User: X-HE-Tag: 1770402323-231544 X-HE-Meta: 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 Ya6WUL/a Two04PzzNhyVXCBmyW+XN/BaMos8fX3ES2J4R41E5P+knyPOYLPL3nz+BV+g3xesF61vRTHs1o0WHDmd+IYC4BYG4DD5ds6wSDkauQ+gf0IQkEVnUVcle3FdQq3q3ax4XQXupVaEj/0WGJgKqY6ECQlCbprcn3xwYgxiA0Fjt54OJ7KUj4eUuZ9f8Rb81EPkA6fYPfuB8jbbJHk/vwnTc0GK3GeigN7uGe4sY+Q9q0U0eUTqhZs6PYyhLcT9YR3HwpTYf8tQ7MNeAUAT+wGyfAYGB4nz4WevdYpmUz+SHP5OZPb/XvNBLdbpWupRBNWSn4po7iYYJJbFaJJgnPxrBSihZOWqzFxRhx+Btetd9qvcrPKDTqnD55+i4x+9bS8L3X2ICLRU+aNCeVCAp2e3NzznboG3JXsiyxPfzcg3S74LJONvie0bYe1QrqFCj7+Z13zdNiFY+R+UgEGR5+v1vATjoaVxkJhItnWmRK5TGr8Low1WENhy/yeu0UkXXfatCe3xUFYQQIDRZ3aLr7YTgqdTEBUpAOZpNVCe64eQlgsZpvneF+mnFjDVv6YEw+Hx3MOggDV1GdcZ1wkMIkZB0ymA3IczouOXx2fsW+3oFRpMkZ2VsxmefwAeLHImNLc9zglP/t0p69ihxXxtMaFcUbeRpjFAtyGtOIAmWTPVjyozoS8Q= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Feb 7, 2026 at 2:08=E2=80=AFAM Zi Yan wrote: > > +willy, david, and others included in Andrew=E2=80=99s mm-commit email. > > On 6 Feb 2026, at 12:40, Mikhail Gavrilov wrote: > > > When vmalloc allocates high-order pages and splits them via split_page(= ), > > tail pages may retain stale page->private values from previous use by t= he > > buddy allocator. > > Do you have a reproducer for this issue? Last time I checked page->privat= e This patch is from previous discussion: https://lore.kernel.org/linux-mm/CABXGCsO3XcXt5GDae7d74ynC6P6G2gLw3ZrwAYvSQ= 3PwP0mGXA@mail.gmail.com/ > usage, I find users clears ->private before free a page. I wonder which o= ne > I was missing. The comment above page_private() does say ->private can > be used on tail pages. If pages are freed with non-zero private in > tail pages, we need to either correct the violating user or clear > all pages ->private in post_alloc_hook() in addition to the head one. > Clearing ->private in split_page() looks like a hack instead of a fix. It looks odd to me too. That bug starts with vmalloc dropping __GFP_COMP in commit 3b8000ae185c, because with __GFP_COMP, the allocator does clean the ->private of tail pages on allocation with prep_compound_page. Without __GFP_COMP, these ->private fields are left as it is.