Re: [PATCH memcg v6] net: set proper memcg for net_init hooks allocations

[Vasily Averin]

On 6/6/22 16:49, Qian Cai wrote:
> On Fri, Jun 03, 2022 at 07:19:43AM +0300, Vasily Averin wrote:

> This triggers a few boot warnings like those.
> 
>  virt_to_phys used for non-linear address: ffffd8efe2d2fe00 (init_net)
>  WARNING: CPU: 87 PID: 3170 at arch/arm64/mm/physaddr.c:12 __virt_to_phys
...
>  Call trace:
>   __virt_to_phys
>   mem_cgroup_from_obj
>   __register_pernet_operations

@@ -1143,7 +1144,13 @@ static int __register_pernet_operations(struct list_head *list,
  		 * setup_net() and cleanup_net() are not possible.
		 */
		for_each_net(net) {
+			struct mem_cgroup *old, *memcg;
+
+			memcg = mem_cgroup_or_root(get_mem_cgroup_from_obj(net));   <<<<  Here
+			old = set_active_memcg(memcg);
 			error = ops_init(ops, net);
+			set_active_memcg(old);
+			mem_cgroup_put(memcg);
...
+static inline struct mem_cgroup *get_mem_cgroup_from_obj(void *p)
+{
+	struct mem_cgroup *memcg;
+
+	rcu_read_lock();
+	do {
+		memcg = mem_cgroup_from_obj(p); <<<<
+	} while (memcg && !css_tryget(&memcg->css));
...
struct mem_cgroup *mem_cgroup_from_obj(void *p)
{
        struct folio *folio;

        if (mem_cgroup_disabled())
                return NULL;

        folio = virt_to_folio(p); <<<< here
...
static inline struct folio *virt_to_folio(const void *x)
{
        struct page *page = virt_to_page(x); <<< here

... (arm64)
#define virt_to_page(x)         pfn_to_page(virt_to_pfn(x))  
...
#define virt_to_pfn(x)          __phys_to_pfn(__virt_to_phys((unsigned long)(x)))
...
phys_addr_t __virt_to_phys(unsigned long x)
{
        WARN(!__is_lm_address(__tag_reset(x)),
             "virt_to_phys used for non-linear address: %pK (%pS)\n",

from arch/x86/include/asm/page.h:
 * virt_to_page(kaddr) returns a valid pointer if and only if
 * virt_addr_valid(kaddr) returns true.

As far as I understand this report means that 'init_net' have incorrect
virtual address on arm64.

Roman, Shakeel, I need your help

Should we perhaps verify kaddr via virt_addr_valid() before using virt_to_page()
If so, where it should be checked?

Thank you,
	Vasily Averin