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Thu, 01 Oct 2026 02:06:01 +0000 X-Mizu-Trace-ID: a8a0d2bf9a452d40 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.100.1.1.11\)) Subject: Re: [PATCH 1/1] mm/memory_hotplug: fix missing rollback in __add_pages() From: Muchun Song In-Reply-To: <20260930160432.5564-1-lance.yang@linux.dev> Date: Thu, 1 Oct 2026 10:05:43 +0800 Cc: david@kernel.org, osalvador@suse.de, akpm@linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20260930160432.5564-1-lance.yang@linux.dev> To: Lance Yang X-Mailer: Apple Mail (2.3901.100.1.1.11) X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D4BB240007 X-Stat-Signature: zekipinwd9kanqjqa1ah75s9npci5wr5 X-Rspam-User: X-HE-Tag: 1790820362-408792 X-HE-Meta: U2FsdGVkX198bZ0Yp2Yv9D5tD1GPmusMMgHEjX/2u4HmKSZvOAxUtecEvE3QASBZI5KF3PH92vybmC/Uijv8ycyrtKpoMeRr5WywQGF/HwUJjFG7n5mOO4tExuvleGiCft5fONFc5KugVJL9xnp6n6Ugn284OwdE1kfKnEhtTPlNbZop2M+GYhu+gkWZanigjNGw1ZDCo9Nsjci8FWb/GFNdRPXoAQ8SORG+KWo6uHvGB/hLfZ0885XYiW9rVZOqTqXuzkCOAzUDB4yZp7+ZLS5ZeShbJaUxxh+ozTo7n1U5WpjtVAQvaEo8lyfWgg5ZeKebVPxXSzY1b8qjHN4lLwSdV47nMlP7sArCGQeFsIPPvXUtqx/Mo2Ex20zUVdT/aOREmuKpXPkfgVjOQUiahcCJrIedu52id0hiSxcDVIXdUZEv0ao3uL/F9aEimL/PKC22SVLCmv+oK/2/X6ABQR3WB02C9CjtFQo6fKwjrHf4w2az0DoTp5WqFd5fNnsDYEvfRH4Ytf4pmP0JI/eqXCvJPrWuru0f/GlZoEF+8257JUPfaUX7RBN5Qjb5xI1MHFfw+FMNSh6poZsem48BRXq+mkex/PUnGfglB6SZBaB6DIG1ua6ksrPBdKqvl4KHh1qR71M4zn5RHnVIhkdkl14gk2sbMPhQYKorarvevX59QhewCGrimEpGWCy8kFz857LCOixoZp9Twb1K7OCTHkhLpQkuAobVbx+U8+VuMUa6utpX8Gk1XNjFLfVtLGkdvk+6ZAvRzU2XHrCVTvg2abIWkFwxcQj2pZgPqjKMkUgN1kXesV9kvSERvgQN+D+RKAQgrrAxJYCZfayjn9GH0ht0ZdNQjm9Ebi1lSQHa5GjMn9LDrmJYjoUu99PwajS6VFT26OOZmtg95uRsGPt7daLY7/FmxsjpUs2OnPvL6ahO/JqIvY4Y6l+NFuJyI4CiEsj+mYDdNCWQqSFhVUw Ev3Gj2Ze KWjPd6p1Pd0n/GkNf1jIH/DnqIs7/jazefky+CdxNHMdAJwO5YUHsYzIKgvYelBhHZXTcEbz5AadqlhzvRyNH6XJVk7tHoYf3r5uegJvdkkeQxtIpUUeErvmP5ChhDyxbuQqzLgE3SS9bKN6U3c1M6NVFBeCEgYB2XdoxU5jhxyT9l/r/+v1IxOn+vqHCRqBbxCSZxPtNbvlYh8qg/ylTzkVwxscP7dagG/NIWoWSiKc4JYZNYWGweo0KuRrwwvCVI5w9qRbDXYX0tUbFOFXXjHOxcy4rut/ZfgfDpGiXAf+8d9uTVURCsvlfgxKZVI1XshAP6B/Dv4xT3pTbVNNToxw66sDdgBQAv7qNPHBHHm4hvCLrCHzr4yMh+Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Oct 1, 2026, at 00:04, Lance Yang wrote: >=20 > __add_pages() returns on a sparse_add_section() failure without = removing > the sections already added in the same request. >=20 > For memremap_pages(), the failed range is not counted in = pgmap->nr_range, > so memunmap_pages() skips it. The sections already added in that range > retain their vmemmap mappings and subsection bits. Retrying a > section-aligned range can then fail with -EEXIST. >=20 > Save the initial PFN and remove [start_pfn, pfn) on failure. For a = vmemmap > population failure, section_activate() already cleans up the current > section, so the rollback excludes it. If the first section fails, > __remove_pages() receives an empty range and does nothing. >=20 > Link: = https://lore.kernel.org/all/BAD58999-1EDD-4A37-ABA0-DB1BD8AB3453@linux.dev= / > Suggested-by: Muchun Song > Signed-off-by: Lance Yang > --- > No Fixes tag, as I couldn't identify the commit that introduced this = issue. Hi Lance, LLMs are quite good at tracing this kind of code history, so I used one to go through the relevant commits and identify the correct Fixes tag. Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") Before that commit, __add_pages() ignored -EEXIST and continued with the remaining sections. After a partial failure, a retry could therefore reuse the vmemmap of sections added by the failed attempt and continue with the later sections. Commit ba72b4c8cf60 made -EEXIST a hard error because sparse_add_section() began using it to report an actual subsection collision. That semantic change was correct, but without rolling back the sections added earlier in the request, stale subsection bits make = the retry stop at the first previously added section. The vmemmap removal infrastructure had already been added by commit 0197518cd367 ("memory-hotplug: remove memmap of sparse-vmemmap"). Therefore, ba72b4c8cf60 appears to be the commit that made this bug observable in the way described by this patch. >=20 > mm/memory_hotplug.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) >=20 > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 796af1028ee2..ca4656698148 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -380,6 +380,7 @@ EXPORT_SYMBOL_GPL(pfn_to_online_page); > int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, > struct mhp_params *params) > { > + const unsigned long start_pfn =3D pfn; > const unsigned long end_pfn =3D pfn + nr_pages; > unsigned long cur_nr_pages; > int err; > @@ -413,8 +414,11 @@ int __add_pages(int nid, unsigned long pfn, = unsigned long nr_pages, > SECTION_ALIGN_UP(pfn + 1) - pfn); > err =3D sparse_add_section(nid, pfn, cur_nr_pages, = altmap, > params->pgmap); > - if (err) > + if (err) { > + __remove_pages(start_pfn, pfn - start_pfn, = altmap, > + params->pgmap); > break; > + } > cond_resched(); > } > vmemmap_populate_print_last(); Acked-by: Muchun Song Thanks, Muchun > --=20 > 2.39.3 >=20