On 10.12.24 10:48, Vlastimil Babka wrote:
On 12/10/24 10:34, David Hildenbrand wrote:In split_large_buddy(), we might call pfn_to_page() on a PFN that might not exist. In corner cases, such as when freeing the highest pageblock in the last memory section, this could result with CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_EXTREME in __pfn_to_section() returning NULL and and __section_mem_map_addr() dereferencing that NULL pointer. Let's fix it, and avoid doing a pfn_to_page() call for the first iteration, where we already have the page. So far this was found by code inspection, but let's just CC stable as the fix is easy. Fixes: fd919a85cd55 ("mm: page_isolation: prepare for hygienic freelists") Reported-by: Vlastimil Babka <vbabka@xxxxxxx> Closes: https://lkml.kernel.org/r/e1a898ba-a717-4d20-9144-29df1a6c8813@xxxxxxx Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Yu Zhao <yuzhao@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
BTW, staring at nr_isolate_pageblock accounting, I just stumbled over prep_move_freepages_block(), and I am not sure about the zone_spans_pfn() checks in there.
With overlapping zones, these are not reliably, which makes me believe that maybe these checks are not required at all. Or that there is a bug. Or that there is some implication that these checks are only required on systems without overlapping zones :)
-- Cheers, David / dhildenb
