Re: [PATCH] memory tier: fix deadlock warning while onlining pages

[Yanfei Xu <yanfei.xu@intel.com>]

On 9/2/2024 9:37 AM, Huang, Ying wrote:
> Yanfei Xu <yanfei.xu@intel.com> writes:
> 
>> [Snip]
>>
>> On 8/30/2024 3:11 PM, Huang, Ying wrote:
>>>> Fixes: 823430c8e9d9 ("memory tier: consolidate the initialization of memory tiers")
>>>> Signed-off-by: Yanfei Xu<yanfei.xu@intel.com>
>>>> ---
>>>>    mm/memory-tiers.c | 1 -
>>>>    1 file changed, 1 deletion(-)
>>>>
>>>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>>>> index 4775b3a3dabe..dddcd6b38e28 100644
>>>> --- a/mm/memory-tiers.c
>>>> +++ b/mm/memory-tiers.c
>>>> @@ -895,7 +895,6 @@ static int __init memory_tier_init(void)
>>>>    	WARN_ON(!node_demotion);
>>>>    #endif
>>>>    -	guard(mutex)(&memory_tier_lock);
>>>>    	/*
>>>>    	 * For now we can have 4 faster memory tiers with smaller adistance
>>>>    	 * than default DRAM tier.
>>> Although it's not absolutely necessary, I still think that it's better
>>> to just revert the locking change of memory_tier_init() in commit
>>> 823430c8e9d9 ("memory tier: consolidate the initialization of memory
>>> tiers").  That is, to use mutex_lock/unlock() and exclude
>>> hotplug_memory_notifier() from the locked region.  Because we will
>>> always hold memory_tier_lock when working on memory tier related data
>>> structures in this way.
>>
>> Thanks for pointing out it. Will do it as below in v2.
>>
>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c
>> index 4775b3a3dabe..ba3738b29cc5 100644
>> --- a/mm/memory-tiers.c
>> +++ b/mm/memory-tiers.c
>> @@ -895,13 +895,14 @@ static int __init memory_tier_init(void)
>>          WARN_ON(!node_demotion);
>>   #endif
>>
>> -       guard(mutex)(&memory_tier_lock);
>> +       mutex_lock(&memory_tier_lock);
>>          /*
>>           * For now we can have 4 faster memory tiers with smaller adistance
>>           * than default DRAM tier.
>>           */
>>          default_dram_type =
>>          mt_find_alloc_memory_type(MEMTIER_ADISTANCE_DRAM,
>>   &default_memory_types);
>> +       mutex_unlock(&memory_tier_lock);
>>          if (IS_ERR(default_dram_type))
>>                  panic("%s() failed to allocate default DRAM tier\n",
>>                  __func__);
>>
>>
> 
> LGTM, feel free to add in the future version.
> 
> Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
> 
Hi Ying,

Thanks for your "Reviewed-by"! I sent the v2 last Friday evening. Could
you please reply to that thread with the "Reviewed-by"? If not, I can
send v3 and include your tag.

Thread name:
8/30/2024, 6:24 PM  [PATCH v2] memory tier: fix deadlock warning while 
onlining pages

Best Regards,
Yanfei