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From: Muchun Song In-Reply-To: Date: Tue, 28 Apr 2026 15:02:14 +0800 Cc: Muchun Song , Andrew Morton , David Hildenbrand , Oscar Salvador , Michael Ellerman , Madhavan Srinivasan , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Nicholas Piggin , Christophe Leroy , aneesh.kumar@linux.ibm.com, joao.m.martins@oracle.com, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <96DB49C7-A7C2-4F53-8321-FF4A4ECDFF95@linux.dev> References: <20260405125240.2558577-1-songmuchun@bytedance.com> <20260405125240.2558577-10-songmuchun@bytedance.com> To: Mike Rapoport X-Migadu-Flow: FLOW_OUT > On Apr 28, 2026, at 14:56, Mike Rapoport wrote: >=20 > On Sun, Apr 05, 2026 at 08:52:00PM +0800, Muchun Song wrote: >> When vmemmap pages allocation or usemap allocation fails, = sparse_init_nid() >> currently only marks the corresponding section as non-present. = However, >> subsequent code like memmap_init() iterating over PFNs does not check = for >> non-present sections, leading to invalid memory access (additional, >> subsection_map_init() accessing the unallocated usemap as well). >>=20 >> It is complex to audit and fix all boot-time PFN iterators to handle = these >> partially initialized sections correctly. Since vmemmap and usemap = allocation >> failures are extremely rare during early boot, the more appropriate = approach >> is to expose the problem as early as possible. >>=20 >> Therefore, use BUG_ON() to panic immediately if allocation fails, = instead of >> attempting a partial recovery that leads to obscure crashes later. >>=20 >> Signed-off-by: Muchun Song >=20 > Acked-by: Mike Rapoport (Microsoft) Thanks. >=20 >> --- >> mm/sparse.c | 37 ++++++++----------------------------- >> 1 file changed, 8 insertions(+), 29 deletions(-) >>=20 >> diff --git a/mm/sparse.c b/mm/sparse.c >> index effdac6b0ab1..5c12b979a618 100644 >> --- a/mm/sparse.c >> +++ b/mm/sparse.c >> @@ -354,19 +354,15 @@ static void __init sparse_init_nid(int nid, = unsigned long pnum_begin, >> unsigned long map_count) >> { >> unsigned long pnum; >> - struct page *map; >> - struct mem_section *ms; >> - >> - if (sparse_usage_init(nid, map_count)) { >> - pr_err("%s: node[%d] usemap allocation failed", = __func__, nid); >> - goto failed; >> - } >>=20 >> + if (sparse_usage_init(nid, map_count)) >> + panic("The node[%d] usemap allocation failed\n", nid); >=20 > Please consider using memblock_alloc_or_panic() in = sparse_usage_init(), it > would simplify the code even more. Hi Mike, Yes. I have several more updates for v2. Please hold off on reviewing the current version to avoid wasting your time; I=E2=80=99ll send the = new one over shortly. Thanks.=