linux-kernel - Re: [PATCH -V2] cxl/region: Support to calculate memory tier abstract distance

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Date: Mon, 17 Jun 2024 10:06:34 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: "Huang, Ying" <ying.huang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>, linux-cxl@...r.kernel.org,
 linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Bharata B Rao <bharata@....com>, Alistair Popple <apopple@...dia.com>,
 "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH -V2] cxl/region: Support to calculate memory tier abstract
 distance



On 6/16/24 7:10 PM, Huang, Ying wrote:
> Alison Schofield <alison.schofield@...el.com> writes:
> 
>> On Tue, Jun 11, 2024 at 01:54:23PM +0800, Ying Huang wrote:
> 
> [snip]
> 
>>> ---
>>>  drivers/cxl/core/region.c | 40 +++++++++++++++++++++++++++++++++++----
>>>  drivers/cxl/cxl.h         |  2 ++
>>>  2 files changed, 38 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>>> index 3c2b6144be23..81d0910c0a02 100644
>>> --- a/drivers/cxl/core/region.c
>>> +++ b/drivers/cxl/core/region.c
>>> @@ -9,6 +9,7 @@
>>>  #include <linux/uuid.h>
>>>  #include <linux/sort.h>
>>>  #include <linux/idr.h>
>>> +#include <linux/memory-tiers.h>
>>>  #include <cxlmem.h>
>>>  #include <cxl.h>
>>>  #include "core.h"
>>> @@ -2304,14 +2305,20 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
>>>  	return true;
>>>  }
>>>  
>>> +static int cxl_region_nid(struct cxl_region *cxlr)
>>> +{
>>> +	struct cxl_region_params *p = &cxlr->params;
>>> +	struct cxl_endpoint_decoder *cxled = p->targets[0];
>>> +	struct cxl_decoder *cxld = &cxled->cxld;
>>> +
>>> +	return phys_to_target_node(cxld->hpa_range.start);
>>> +}
>>> +
>>
>> I believe it's OK to send a resource_size_t to phys_to_target_node()
>> like this:
>>
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -2308,10 +2308,8 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
>>  static int cxl_region_nid(struct cxl_region *cxlr)
>>  {
>>         struct cxl_region_params *p = &cxlr->params;
>> -       struct cxl_endpoint_decoder *cxled = p->targets[0];
>> -       struct cxl_decoder *cxld = &cxled->cxld;
>>
>> -       return phys_to_target_node(cxld->hpa_range.start);
>> +       return phys_to_target_node(p->res->start);
>>  }
>>
> 
> Read the related code again, it appears that there's a theoretical race
> condition here.  The register_memory_notifier() is called in
> devm_cxl_add_region(), where p->targets[] and p->res haven't been
> setupped yet.  And, IIUC, p->targets[] or p->res may be gone during the
> life cycle of regions too.  If so, we need to use
> guard(rwsem_read)(&cxl_region_rwsem) to protect p->targets[] and p->res
> references.  Because the memory notifier may be called for other nodes
> online/offline.

You mind sending a patch? :)

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