Re: [PATCH] drivers/base/memory: set mem->altmap after successful device registration

[Georgi Djakov <georgi.djakov@oss.qualcomm.com>]

Hi David,

On 5/13/2026 4:20 PM, David Hildenbrand (Arm) wrote:
> On 5/13/26 15:14, David Hildenbrand (Arm) wrote:
>> On 5/13/26 15:09, Georgi Djakov wrote:
>>> If __add_memory_block() fails at xa_store() (under memory pressure
>>> for example), device_unregister() is called, which eventually
>>> triggers memory_block_release() with mem->altmap still set, causing
>>> a WARN_ON(mem->altmap).
>>>
>>> WARNING: CPU: 1 PID: 76 at drivers/base/memory.c:96 memory_block_release+0x28/0x30
>>> Call trace:
>>>  memory_block_release+0x28/0x30 (P)
>>>  kobject_put+0xc8/0x1bc
>>>  device_unregister+0x2c/0x68
>>>  add_memory_block+0x1b4/0x214
>>>  create_memory_block_devices+0x9c/0xfc
>>>  create_altmaps_and_memory_blocks+0x130/0x1cc
>>>  add_memory_resource+0x10c/0x21c
>>>  add_memory_driver_managed+0xb8/0xe8
>>>  virtio_mem_add_memory+0xa4/0x194 [virtio_mem]
>>>  virtio_mem_sbm_plug_and_add_mb+0xc8/0x16c [virtio_mem]
>>>  virtio_mem_run_wq+0xea8/0x1088 [virtio_mem]
>>>  process_scheduled_works+0x18c/0x300
>>>  worker_thread+0x1dc/0x2b8
>>>  kthread+0x1ac/0x1f4
>>>  ret_from_fork+0x10/0x20
>>>
>>> Fix this by delaying the assignment of mem->altmap until after
>>> __add_memory_block() has succeeded.
>>
>> Something does not add up here. How do you get an altmap with virtio-mem?
> 
> That patch itself makes sense, but the callchain does not make sense.
> 
> virtio_mem does not set MHP_MEMMAP_ON_MEMORY, so it should never reach
> create_altmaps_and_memory_blocks()?

I have some out of tree virtio_mem patches on top that helped to trigger
this. Sorry for not mentioning it. Should i remove the callchain from the
commit text to avoid confusion?

Thanks,
Georgi