Re: [PATCH v2 3/3] drivers/base/memory: fix locking for poison accounting lookup

[Miaohe Lin]

On 2026/4/28 19:40, Muchun Song wrote:
> 
> 
>> On Apr 28, 2026, at 19:37, Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>>
>> On 2026/4/28 16:52, Muchun Song wrote:
>>> memblk_nr_poison_inc() and memblk_nr_poison_sub() call
>>> find_memory_block_by_id(), which requires device_hotplug_lock to
>>> serialize the xarray lookup against memory block removal.
>>>
>>> Take device_hotplug_lock around the lookup and nr_hwpoison update so
>>> the memory block cannot disappear between xa_load() and get_device().
>>>
>>> Fixes: 5033091de814 ("mm/hwpoison: introduce per-memory_block hwpoison counter")
>>> Cc: stable@xxxxxxxxxxxxxxx
>>> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>>
>> Thanks for update.
>>
>>> ---
>>> drivers/base/memory.c | 10 ++++++++--
>>> 1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>>> index 6981b55d582a..f76aee29e9a5 100644
>>> --- a/drivers/base/memory.c
>>> +++ b/drivers/base/memory.c
>>> @@ -1228,23 +1228,29 @@ int walk_dynamic_memory_groups(int nid, walk_memory_groups_func_t func,
>>> void memblk_nr_poison_inc(unsigned long pfn)
>>> {
>>> 	const unsigned long block_id = pfn_to_block_id(pfn);
>>> - 	struct memory_block *mem = find_memory_block_by_id(block_id);
>>> + 	struct memory_block *mem;
>>>
>>> + 	lock_device_hotplug();
>>
>> memblk_nr_poison_inc() and memblk_nr_poison_sub() are both called from memory_failure() context.
>> I'm afraid if memory_failure() is triggered while lock_device_hotplug is held, it will lead to
>> deadlock. Or am I miss something?
> 
> I am curious is there any place where memory_failure() is called with holding lock_device_hotplug?

Sorry for dumb scenario, I was a bit too presumptuous. But there might be another possible deadlock:

remove_memory
  lock_device_hotplug <-- first called here
  try_remove_memory
    remove_memory_block_devices
      num_poisoned_pages_sub
        memblk_nr_poison_sub
          lock_device_hotplug <-- deadlock here

Hope I'm not mistaken again. :)

Thank.
.