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allocated PFNs and causes free page leaks. Fix it b= y >>> calling release_free_list() in the error path. >>> >>> The issue is reported by Sashiko[1]. >>=20 >> So this? >> Reported-by: Sashiko >>=20 >>> Fixes: e98337d11bbd ("mm/contig_alloc: support __GFP_COMP") >>> Link: https://sashiko.dev/#/patchset/20260628-keep-subpage-private-zero= -at-free-v1-0-f4ce3930d10f@nvidia.com [1] >>> Signed-off-by: Zi Yan >>> Cc: stable@vger.kernel.org >>=20 >> Hm well, it's a path that warns, can only happen due to a development er= ror? >> Not sure we care about stable then. Anyway. >>=20 > > If someone would run into the WARN we would already be in Fixes: territor= y. > > it's a path that should never be executed. If it does, the real issue mus= t be fixed. > > So (a) I don't think this is stable material (b) I am skeptical that this= is > even a Fixes and (c) I am wondering whether we should touch this *at all*= . > > :) I looked at the code again and agree with you that the code is not reachable and the fix should not be in the WARN path. Theoretically, if order =3D ilog2(end - start) is smaller than MAX_PAGE_ORDER, find_large_buddy() can return an outer_start smaller than start, leading to this WARN path. But currently alloc_contig_frozen_range() with __GFP_COMP is used by gigantic hugetlb, thus that is not possible. How about 1. making sure order is bigger or equal to MAX_PAGE_ORDER, 2. adding a comment in the WARN path to prevent someone else trying to fix WARN path if Sashiko reports this again like the patch below? diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ee902a468c2f..e87d3fced9d4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -7130,8 +7130,13 @@ int alloc_contig_frozen_range_noprof(unsigned long s= tart, unsigned long end, * In contrast to the buddy, we allow for orders here that exceed * MAX_PAGE_ORDER, so we must manually make sure that we are not * exceeding the maximum folio order. + * + * The order cannot be smaller than MAX_PAGE_ORDER either to prevent a + * potential mismatch between the requested range and the allocated + * range that leads to an allocation failure. */ - if (WARN_ON_ONCE((gfp_mask & __GFP_COMP) && order > MAX_FOLIO_ORDER)) + if (WARN_ON_ONCE((gfp_mask & __GFP_COMP) && + (order > MAX_FOLIO_ORDER || order < MAX_PAGE_ORDER)) return -EINVAL; =20 gfp_mask =3D current_gfp_context(gfp_mask); @@ -7235,6 +7240,7 @@ int alloc_contig_frozen_range_noprof(unsigned long st= art, unsigned long end, check_new_pages(head, order); prep_new_page(head, order, gfp_mask, 0); } else { + /* Fix the caller if this is reachable */ ret =3D -EINVAL; WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n", start, end, outer_start, outer_end); --=20 Best Regards, Yan, Zi