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From:   Tarun Sahu <tsahu@linux.ibm.com>
To:     nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, dave.jiang@intel.com,
        dan.j.williams@intel.com, vishal.l.verma@intel.com,
        aneesh.kumar@linux.ibm.com, jaypatel@linux.ibm.com
Subject: Re: [PATCH v3] dax/kmem: Pass valid argument to
 memory_group_register_static
In-Reply-To: <20230621155025.370672-1-tsahu@linux.ibm.com>
References: <20230621155025.370672-1-tsahu@linux.ibm.com>
Date:   Fri, 30 Jun 2023 09:11:43 +0530
Message-ID: <87cz1daa6g.fsf@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk


Hi,

This is just a gentle reminder, If any other information is needed.

Tarun Sahu <tsahu@linux.ibm.com> writes:

> memory_group_register_static takes maximum number of pages as the argument
> while dev_dax_kmem_probe passes total_len (in bytes) as the argument.
>
> IIUC, I don't see any crash/panic impact as such. As,
> memory_group_register_static just set the max_pages limit which is used in
> auto_movable_zone_for_pfn to determine the zone.
>
> which might cause these condition to behave differently,
>
> This will be true always so jump will happen to kernel_zone
>     ...
>     if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
>         goto kernel_zone;
>
>     ...
>     kernel_zone:
>         return default_kernel_zone_for_pfn(nid, pfn, nr_pages);
>
> Here, In below, zone_intersects compare range will be larger as nr_pages
> will be higher (derived from total_len passed in dev_dax_kmem_probe).
>
>     ...
>     static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
>     		unsigned long nr_pages)
>     {
>     	struct pglist_data *pgdat = NODE_DATA(nid);
>     	int zid;
>
>     	for (zid = 0; zid < ZONE_NORMAL; zid++) {
>     		struct zone *zone = &pgdat->node_zones[zid];
>
>     		if (zone_intersects(zone, start_pfn, nr_pages))
>     			return zone;
>     	}
>
>     	return &pgdat->node_zones[ZONE_NORMAL];
>     }
>
> Incorrect zone will be returned here, which in later time might cause bigger
> problem.
>
> Fixes: eedf634aac3b ("dax/kmem: use a single static memory group for a single probed unit")
> Signed-off-by: Tarun Sahu <tsahu@linux.ibm.com>
> Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
> V3<-V2
> 1. Removed skip characters.
>
> V2<-V1
> 1. Added more details to commit message
>
>
>  drivers/dax/kmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index 7b36db6f1cbd..898ca9505754 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -99,7 +99,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  	if (!data->res_name)
>  		goto err_res_name;
>  
> -	rc = memory_group_register_static(numa_node, total_len);
> +	rc = memory_group_register_static(numa_node, PFN_UP(total_len));
>  	if (rc < 0)
>  		goto err_reg_mgid;
>  	data->mgid = rc;
> -- 
> 2.31.1


~Tarun