[PATCH] mm/page_alloc: release isolated freepages on compound range mismatch

[Zhenghui Hao]

alloc_contig_frozen_range_noprof() isolates [outer_start, outer_end)
before checking whether a __GFP_COMP request exactly matches the
allocated range.  If it does not, the function returns -EINVAL without
releasing cc.freepages, leaking the isolated pages.

Call release_free_list() before returning -EINVAL, while the pageblock
is still isolated, matching the cleanup already used when
isolate_freepages_range() fails.

Use WARN_ONCE() as well: the condition is reachable through the exported
API, and repeated invalid calls should not flood dmesg.

Tested with an order-9 free pageblock and a one-page __GFP_COMP
subrange:
  before: free_buddy=0, leaked=512/512
  after:  free_buddy=1, leaked=0/512

Fixes: e98337d11bbdf ("mm/contig_alloc: support __GFP_COMP")
Signed-off-by: Zhenghui Hao <zhenghui.hao@xxxxxx>
---
 mm/compaction.c | 2 +-
 mm/internal.h   | 2 ++
 mm/page_alloc.c | 9 +++++++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index f1b2060eb201..11ec991206bb 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -89,7 +89,7 @@ static struct page *mark_allocated_noprof(struct page *page, unsigned int order,
 }
 #define mark_allocated(...)	alloc_hooks(mark_allocated_noprof(__VA_ARGS__))
 
-static unsigned long release_free_list(struct list_head *freepages)
+unsigned long release_free_list(struct list_head *freepages)
 {
 	int order;
 	unsigned long high_pfn = 0;
diff --git a/mm/internal.h b/mm/internal.h
index 566cbd2dce48..364b288a0e2c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -880,6 +880,8 @@ int
 isolate_migratepages_range(struct compact_control *cc,
 			   unsigned long low_pfn, unsigned long end_pfn);
 
+unsigned long release_free_list(struct list_head *freepages);
+
 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
 
 struct cma;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a8cac5e01066..6913e0f94540 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7400,9 +7400,14 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end,
 		check_new_pages(head, order);
 		prep_new_page(head, order, gfp_mask, ALLOC_DEFAULT);
 	} else {
+		/*
+		 * isolate_freepages_range() has removed the pages from the buddy
+		 * allocator.  Put them back before undoing pageblock isolation.
+		 */
+		release_free_list(cc.freepages);
 		ret = -EINVAL;
-		WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
-		     start, end, outer_start, outer_end);
+		WARN_ONCE(1, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
+			  start, end, outer_start, outer_end);
 	}
 done:
 	undo_isolate_page_range(start, end);
-- 
2.53.0