Re: [PATCH v2 5/5] mm/page_alloc.c: avoid allocating highmem pages via alloc_pages_exact[_nid]

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On 02.09.21 14:12, Miaohe Lin wrote:
Don't use with __GFP_HIGHMEM because page_address() cannot represent
highmem pages without kmap(). Newly allocated pages would leak as
page_address() will return NULL for highmem pages here. But It works
now because the callers do not specify __GFP_HIGHMEM now.

Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
  mm/page_alloc.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9c09dcb24149..e1d0e27d005a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5614,8 +5614,8 @@ void *alloc_pages_exact(size_t size, gfp_t gfp_mask)
  	unsigned int order = get_order(size);
  	unsigned long addr;
- if (WARN_ON_ONCE(gfp_mask & __GFP_COMP))
-		gfp_mask &= ~__GFP_COMP;
+	if (WARN_ON_ONCE(gfp_mask & (__GFP_COMP | __GFP_HIGHMEM)))
+		gfp_mask &= ~(__GFP_COMP | __GFP_HIGHMEM);
addr = __get_free_pages(gfp_mask, order);
  	return make_alloc_exact(addr, order, size);
@@ -5639,8 +5639,8 @@ void * __meminit alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask)
  	unsigned int order = get_order(size);
  	struct page *p;
- if (WARN_ON_ONCE(gfp_mask & __GFP_COMP))
-		gfp_mask &= ~__GFP_COMP;
+	if (WARN_ON_ONCE(gfp_mask & (__GFP_COMP | __GFP_HIGHMEM)))
+		gfp_mask &= ~(__GFP_COMP | __GFP_HIGHMEM);
p = alloc_pages_node(nid, gfp_mask, order);
  	if (!p)


Ideally we would convert this WARN_ON_ONCE() to pr_warn_once(), but I guess this really never ever happens on a production system and would get caught early while testing.

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

--
Thanks,

David / dhildenb





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