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

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

[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__);


Best Regards,
Yanfei

> 
> --
> Best Regards,
> Huang, Ying