[PATCH RFC] mm: warn potential return NULL for kmalloc_array and kvmalloc_array with __GFP_NOFAIL

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

Overflow in this context is highly unlikely. However, allocations using
GFP_NOFAIL are guaranteed to succeed, so checking the return value is
unnecessary. One option to fix this is allowing memory allocation with
an overflowed size, but it seems pointless. Let's at least issue a
warning. Likely BUG_ON() seems better as anyway we can't fix it?

Cc: Michal Hocko <mhocko@suse.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 include/linux/slab.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index a332dd2fa6cd..c6aec311864f 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -692,8 +692,10 @@ static inline __alloc_size(1, 2) void *kmalloc_array_noprof(size_t n, size_t siz
 {
 	size_t bytes;
 
-	if (unlikely(check_mul_overflow(n, size, &bytes)))
+	if (unlikely(check_mul_overflow(n, size, &bytes))) {
+		WARN_ON(flags & __GFP_NOFAIL);
 		return NULL;
+	}
 	if (__builtin_constant_p(n) && __builtin_constant_p(size))
 		return kmalloc_noprof(bytes, flags);
 	return kmalloc_noprof(bytes, flags);
@@ -794,8 +796,10 @@ kvmalloc_array_node_noprof(size_t n, size_t size, gfp_t flags, int node)
 {
 	size_t bytes;
 
-	if (unlikely(check_mul_overflow(n, size, &bytes)))
+	if (unlikely(check_mul_overflow(n, size, &bytes))) {
+		WARN_ON(flags & __GFP_NOFAIL);
 		return NULL;
+	}
 
 	return kvmalloc_node_noprof(bytes, flags, node);
 }
-- 
2.34.1