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From: Muchun Song In-Reply-To: <20260525144948.15e51eb81151e498cc2af999@linux-foundation.org> Date: Tue, 26 May 2026 10:01:30 +0800 Cc: Muchun Song , Oscar Salvador , David Hildenbrand , Kiryl Shutsemau , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260525025213.2229628-1-songmuchun@bytedance.com> <20260525144948.15e51eb81151e498cc2af999@linux-foundation.org> To: Andrew Morton X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 82BBD18000A X-Stat-Signature: d3dy6k4nnu1wu7ohdx8mbtpmwq6yrdys X-Rspam-User: X-HE-Tag: 1779760951-126710 X-HE-Meta: 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 tgqulqGo yh3xdgXiQRuKeQTaZemiGtW4AoSVlzBlpLI4mpY1NlEbRrahXChwOTRyXoyDWBx64vhhN9ZLrHfGQSN39WhcWR93mCU0kBfguQhaldZVwdXdgSDGO19kN5rRtGDHO1jwzGBu7NmUYW6xkXjnUxHCtuA1nLvNGy8QGqXatj7py55cZmsvN8DM0qN+Na6lDrcG5qqBtg/LxOk63Jq3Dqiu5TKE6bOE69FYWYiRMVdx+kHQx1Qy79yQ4Sn3Ieq2pUbvuzUR5NIvoRLMKDvBpiCVKTmOgbUbOhz06VLV5I6XGsfQPNUawaaAEESW7bLhgHlVTwrDFYcwxqnrLXo1JCViwsjWG1GEx+UCmhmGyJv6Fkdm4ffsPeg2t+aoAgbOHOYq1vy3KU1/buXyjmOMmVDtCBDfBAso+Ny0wRaHwnR4NgLuLp/A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On May 26, 2026, at 05:49, Andrew Morton = wrote: >=20 > On Mon, 25 May 2026 10:52:13 +0800 Muchun Song = wrote: >=20 >> vmemmap_restore_pte() rebuilds restored vmemmap pages from a >> tail-page template derived from compound_head(). This is wrong when = the >> current PTE already maps a page whose contents are not tail-page >> metadata. >>=20 >> In the rollback path of vmemmap_remap_free(), the first restored PTE = is >> backed by vmemmap_head and contains head-page metadata. = Reconstructing >> that page from a tail-page template overwrites the head-page state = and >> corrupts the restored vmemmap page. >>=20 >> Fix this by copying the full page from the page currently mapped by = the >> PTE. Also pass vmemmap_tail to the rollback walk so only PTEs backed = by >> the shared tail page are restored, while the head PTE remains mapped = to >> vmemmap_head. Add VM_WARN_ON_ONCE() checks for unexpected cases. >=20 > Queued in mm-hotfixes, thanks. >=20 >> Fixes: c0b495b91a47 ("mm/hugetlb: refactor code around vmemmap_walk") >=20 > A "refactoring" patch caused a regression? Ouch. Yes. >=20 > This patch caused Sashiko to identify a possible pre-existing mem > hotplug race: > = https://sashiko.dev/#/patchset/20260525025213.2229628-1-songmuchun@bytedan= ce.com I think it is a false positive since hugetlb pages cannot be freed to buddy allocator, we cannot race with memory hot remove. Muchun, Thanks.