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s=arc-20220608; t=1771373779; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ecctfRFqqqU5IDfd4MSEa+PI90gGGEgsBGWlOD5z63A=; b=PTCnEqtoQQWjUGOsLC/dFWTair2GpE8tBGAINOZWzGPsK5hHx6eyOuOZC+O5UsImKFvmfL QfhqX85697/UhFhssb0WHCjNMO06oFutiDp5vlc50TBEeRn1gn1+iyNWB/cJS7GXhUuw1d cKBZ7rcDwI9L2o/EUrUlt4Fz4UUwjbg= Received: from [IPv6:::1] (localhost [127.0.0.1]) by gate.crashing.org (8.18.1/8.18.1/Debian-2) with ESMTP id 61I0FxLB472134; Tue, 17 Feb 2026 18:16:06 -0600 Message-ID: <4d93284349178a783725539b66dca25725fa779d.camel@kernel.crashing.org> Subject: Re: [PATCH v2] mm: Fix memblock_free_late() when using deferred struct page From: Benjamin Herrenschmidt To: linux-mm@kvack.org Cc: Mike Rapoport Date: Wed, 18 Feb 2026 11:15:59 +1100 In-Reply-To: <14295eba34f10f5896e6cb7d3e1abd36199cd918.camel@kernel.crashing.org> References: <14295eba34f10f5896e6cb7d3e1abd36199cd918.camel@kernel.crashing.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.3-0ubuntu1.1 MIME-Version: 1.0 X-Stat-Signature: fgy9mpoknmwnqn1rf1dkqnyu3np7abrs X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A95AE2000A X-HE-Tag: 1771373777-365667 X-HE-Meta: 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 5U4kFvW3 dZjwqT9WhsD8CQFsA/+HFA6W5UJr4C7K9u7g0doXzintH4g3EycwCUsWn30cdB1n7rR8oxHpv/4nFHhFJ7q1pptI4vx6WOrSeM8prjQ/ajKQdng+C+NBNfNN3dw== 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 Wed, 2026-02-18 at 08:47 +1100, Benjamin Herrenschmidt wrote: > There is definitely something fishy going on, though I don't know what, > as the page is reserved so it should *not* be touched by the deferred > initialization... Could there be an issue by which we incorrectly go > look at the head page (which hasn't been initialized) of a *potential* > compound/huge page ? So ... not 100% certain but I see this in __free_one_page(): buddy =3D find_buddy_page_pfn(page, pfn, order, &buddy_pfn); Then goes do things with the buddy. find_buddy_page_pfn() is (stripping comments): static inline unsigned long __find_buddy_pfn(unsigned long page_pfn, unsigned int order) { return page_pfn ^ (1 << order); } static inline struct page *find_buddy_page_pfn(struct page *page, unsigned long pfn, unsigned int order, unsigned long *buddy_pfn) { unsigned long __buddy_pfn =3D __find_buddy_pfn(pfn, order); struct page *buddy; buddy =3D page + (__buddy_pfn - pfn); if (buddy_pfn) *buddy_pfn =3D __buddy_pfn; if (page_is_buddy(page, buddy, order)) return buddy; return NULL; } Now what happens if order is 0, page_pfn is a reserved page whose "buddy" isn't reserved ... and whose struct page is not initialized yet due to deferral ? Unless I'm mistaken, we are going to poke around at uninitialized struct pages and things can go anywhere from there, can't they ? Or am I missing a piece of the puzzle ? Cheers, Ben.