mm/slab: Add kvfree_atomic() helper

kvmalloc() now supports non-sleeping GFP flags, including
the vmalloc fallback path. This means it may return vmalloc
memory even for GFP_ATOMIC and GFP_NOWAIT allocations.

Freeing such memory with kvfree() may then end up calling
vfree(), which is not safe for non-sleeping contexts.

Introduce kvfree_atomic() helper for such cases. It mirrors
kvfree(), but uses vfree_atomic() for vmalloced memory.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Acked-by: Harry Yoo (Oracle) <harry@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/linux/slab.h

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 15a60b5..2b5ab48 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -1234,6 +1234,9 @@ void *kvrealloc_node_align_noprof(const void *p, size_t size, unsigned long alig
 extern void kvfree(const void *addr);
 DEFINE_FREE(kvfree, void *, if (!IS_ERR_OR_NULL(_T)) kvfree(_T))
 
+extern void kvfree_atomic(const void *addr);
+DEFINE_FREE(kvfree_atomic, void *, if (!IS_ERR_OR_NULL(_T)) kvfree_atomic(_T))
+
 extern void kvfree_sensitive(const void *addr, size_t len);
 
 unsigned int kmem_cache_size(struct kmem_cache *s);

mm/slub.c

diff --git a/mm/slub.c b/mm/slub.c
index 0baa906..8f90045 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -6883,6 +6883,22 @@ void kvfree(const void *addr)
 EXPORT_SYMBOL(kvfree);
 
 /**
+ * kvfree_atomic() - Free memory.
+ * @addr: Pointer to allocated memory.
+ *
+ * Same as kvfree(), but uses vfree_atomic() for vmalloc
+ * backed memory. Must not be called from NMI context.
+ */
+void kvfree_atomic(const void *addr)
+{
+	if (is_vmalloc_addr(addr))
+		vfree_atomic(addr);
+	else
+		kfree(addr);
+}
+EXPORT_SYMBOL(kvfree_atomic);
+
+/**
  * kvfree_sensitive - Free a data object containing sensitive information.
  * @addr: address of the data object to be freed.
  * @len: length of the data object.