Arm64 crash while reading memory sysfs

[Qian Cai]

On 5/27/2021 12:22 PM, Mike Rapoport wrote:
> On Thu, May 27, 2021 at 10:33:13AM -0400, Qian Cai wrote:
>>
>>
>> On 5/27/2021 4:56 AM, Mike Rapoport wrote:
>>> Let's drop memblock=debug for now and add this instead:
>>
>> [    0.000000][    T0] Booting Linux on physical CPU 0x0000000000 [0x503f0002]
>> [    0.000000][    T0] Linux version 5.13.0-rc3-next-20210526+ (root at admin5) (gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #31 SMP Thu May 27 12:32:40 UTC 2021
>> [    0.000000][    T0] Inode-cache hash table entries: 4194304 (order: 9, 33554432 bytes, linear)
>> [    0.000000][    T0] mem auto-init: stack:off, heap alloc:on, heap free:off
>> [    0.000000][    T0] MEMBLOCK configuration:
>> [    0.000000][    T0]  memory size = 0x0000001ff0000000 reserved size = 0x0000000421e33ae8
>> [    0.000000][    T0]  memory.cnt  = 0xc
>> [    0.000000][    T0] Memory: 777216K/133955584K available (17984K kernel code, 118722K rwdata, 4416K rodata, 6080K init, 67276K bss, 17379072K reserved, 0K cma-reserved)
> 
> I still cannot understand where most of the memory disappeared, but it
> seems entirely different issue.

Interesting, it seems those memory did come back after booting.

# cat /proc/meminfo
MemTotal:       116656448 kB
MemFree:        110464000 kB
MemAvailable:   101919872 kB
Buffers:           16320 kB
Cached:           118912 kB
SwapCached:         3136 kB
Active:            63360 kB
Inactive:         199936 kB
Active(anon):       9792 kB
Inactive(anon):   132480 kB
Active(file):      53568 kB
Inactive(file):    67456 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       8388544 kB
SwapFree:        8344704 kB
Dirty:                 0 kB
Writeback:             0 kB
AnonPages:        125056 kB
Mapped:            44992 kB
Shmem:             14784 kB
KReclaimable:      92160 kB
Slab:            4943424 kB
SReclaimable:      92160 kB
SUnreclaim:      4851264 kB
KernelStack:       24832 kB
PageTables:        10240 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    66716736 kB
Committed_AS:     708096 kB
VmallocTotal:   133143461888 kB
VmallocUsed:       49600 kB
VmallocChunk:          0 kB
Percpu:            45056 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
FileHugePages:         0 kB
FilePmdMapped:         0 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:     524288 kB
Hugetlb:               0 kB

>  
>>> Sorry, I've missed that the BUG is apparently triggered for pfn + i. Can
>>> you please try this instead:
>>
>> [  259.216661][ T1417] test_pages_in_a_zone: pfn 8000 is not valid
>> [  259.226547][ T1417] page:00000000f4aa8c5c is uninitialized and poisoned
>> [  259.226560][ T1417] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
> 
> Can you please try Anshuman's patch "arm64/mm: Drop HAVE_ARCH_PFN_VALID":
> 
> https://lore.kernel.org/lkml/1621947349-25421-1-git-send-email-anshuman.khandual@arm.com
> 
> It seems to me that the check for memblock_is_memory() in
> arm64::pfn_valid() is what makes init_unavailable_range() to bail out for
> section parts that are not actually populated and then we have
> VM_BUG_ON_PAGE(PagePoisoned(p)) for these pages.

That patch fixed it.