Re: [next] arm64: boot failed - next-20220606

[Vasily Averin]

Dear ARM developers,
could you please help me to find the reason of this problem?

On 6/7/22 18:29, Naresh Kamboju wrote:
> On Tue, 7 Jun 2022 at 19:47, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>>
>> On Tue, Jun 7, 2022 at 3:28 AM Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> wrote:
>>>
>>> Hi Shakeel,
>>>
>>>>>> Can you test v5.19-rc1, please?  If that does not fail, then you could
>>>>>> bisect between that and next-20220606 ...
>>>>>>
>>>>>
>>>>> This is already reported at
>>>>> https://lore.kernel.org/all/Yp4F6n2Ie32re7Ed@qian/ and I think we know
>>>>> the underlying issue (which is calling virt_to_page() on a vmalloc
>>>>> address).
>>>>
>>>> Sorry, I might be wrong. Just checked the stacktrace again and it
>>>> seems like the failure is happening in early boot in this report.
>>>> Though the error "Unable to handle kernel paging request at virtual
>>>> address" is happening in the function mem_cgroup_from_obj().
>>>>
>>>> Naresh, can you repro the issue if you revert the patch "net: set
>>>> proper memcg for net_init hooks allocations"?
>>>
>>> yes. You are right !
>>> 19ee3818b7c6 ("net: set proper memcg for net_init hooks allocations")
>>> After reverting this single commit I am able to boot arm64 successfully.
>>>
>>> Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
>>>
>>
>> Can you please run script/faddr2line on "mem_cgroup_from_obj+0x2c/0x120"?
> 
> ./scripts/faddr2line vmlinux  mem_cgroup_from_obj+0x2c/0x120
> mem_cgroup_from_obj+0x2c/0x120:
> mem_cgroup_from_obj at ??:?
> 
> Please find the following artifacts which are causing kernel crashes.
> 
> vmlinux: https://builds.tuxbuild.com/2ABl8X9kHAAU5MlL3E3xExHFrNy/vmlinux.xz
> System.map: https://builds.tuxbuild.com/2ABl8X9kHAAU5MlL3E3xExHFrNy/System.map

Dear Naresh,
thank you very much

mem_cgroup_from_obj():
ffff80000836cf40:       d503245f        bti     c
ffff80000836cf44:       d503201f        nop
ffff80000836cf48:       d503201f        nop
ffff80000836cf4c:       d503233f        paciasp
ffff80000836cf50:       d503201f        nop
ffff80000836cf54:       d2e00021        mov     x1, #0x1000000000000            // #281474976710656
ffff80000836cf58:       8b010001        add     x1, x0, x1
ffff80000836cf5c:       b25657e4        mov     x4, #0xfffffc0000000000         // #-4398046511104
ffff80000836cf60:       d34cfc21        lsr     x1, x1, #12
ffff80000836cf64:       d37ae421        lsl     x1, x1, #6
ffff80000836cf68:       8b040022        add     x2, x1, x4
ffff80000836cf6c:       f9400443        ldr     x3, [x2, #8]

x5 : ffff80000a96f000 x4 : fffffc0000000000 x3 : ffff80000ad5e680
x2 : fffffe00002bc240 x1 : 00000200002bc240 x0 : ffff80000af09740

x0 = 0xffff80000af09740 is an argument of mem_cgroup_from_obj()
according to System.map it is init_net

This issue is caused by calling virt_to_page() on address of static variable init_net.
Arm64 consider that addresses of static variables are not valid virtual addresses.
On x86_64 the same API works without any problem.

Unfortunately I do not understand the cause of the problem.
I do not see any bugs in my patch.
I'm using an existing API, mem_cgroup_from_obj(), to find the memory cgroup used
to account for the specified object.
In particular, in the current case, I wanted to get the memory cgroup of the
specified network namespace by the name taken from for_each_net(). 
The first object in this list is the static structure unit_net

On x86_64 I can translate its address to page:

crash> p &init_net
$1 = (struct net *) 0xffffffff90c7bdc0 <init_net>
crash> vtop 0xffffffff90c7bdc0
VIRTUAL           PHYSICAL        
ffffffff90c7bdc0  402c7bdc0       

PGD DIRECTORY: ffffffff8fe10000
PAGE DIRECTORY: 401e15067
   PUD: 401e15ff0 => 401e16063
   PMD: 401e16430 => 8000000402c000e3
  PAGE: 402c00000  (2MB)

      PTE         PHYSICAL   FLAGS
8000000402c000e3  402c00000  (PRESENT|RW|ACCESSED|DIRTY|PSE|NX)

      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
fffff227d00b1ec0 402c7b000                0        0  1 17ffffc0001000 reserved

However, as far as I understand this does not work for arm64.
Could you please help me to understand what is wrong here?

Below are:
 link to my patch:
https://lore.kernel.org/all/20220603182442.63750C385B8@xxxxxxxxxxxxxxx/
 and the quote of my investigation of similar report:
https://lore.kernel.org/all/Yp4F6n2Ie32re7Ed@qian/

> 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",
...
virt_to_phys used for non-linear address: ffffd8efe2d2fe00 (init_net)

Thank you,
	Vasily Averin