On Mon, 8 Feb 2021 13:08:20 +0200 Mike Rapoport rppt@kernel.org wrote:
There could be struct pages that are not backed by actual physical memory. This can happen when the actual memory bank is not a multiple of SECTION_SIZE or when an architecture does not register memory holes reserved by the firmware as memblock.memory.
Such pages are currently initialized using init_unavailable_mem() function that iterates through PFNs in holes in memblock.memory and if there is a struct page corresponding to a PFN, the fields of this page are set to default values and it is marked as Reserved.
init_unavailable_mem() does not take into account zone and node the page belongs to and sets both zone and node links in struct page to zero.
On a system that has firmware reserved holes in a zone above ZONE_DMA, for instance in a configuration below:
# grep -A1 E820 /proc/iomem 7a17b000-7a216fff : Unknown E820 type 7a217000-7bffffff : System RAM
unset zone link in struct page will trigger
VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link in struct page) in the same pageblock.
...
Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
What are your thoughts on the priority of this (rather large!) fix? Are such systems sufficiently common to warrant a 5.11 merge? -stable?