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

[Muchun Song]




> On Apr 28, 2026, at 20:34, Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
> 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

Passing pfn = -1 here.

>        memblk_nr_poison_sub
>          lock_device_hotplug <-- deadlock here

No. Can’t reach here. No deadlock.

Thanks.

> 
> Hope I'm not mistaken again. :)
> 
> Thank.
> .