linux-kernel - Re: [PATCH V3 04/20] nvdimm/label: Update mutex

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Message-ID: <b66e4c0b-a82f-4c18-8e8b-ba37b6551964@intel.com>
Date: Fri, 19 Sep 2025 16:50:59 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Neeraj Kumar <s.neeraj@...sung.com>, linux-cxl@...r.kernel.org,
 nvdimm@...ts.linux.dev, linux-kernel@...r.kernel.org, gost.dev@...sung.com
Cc: a.manzanares@...sung.com, vishak.g@...sung.com, neeraj.kernel@...il.com,
 cpgs@...sung.com
Subject: Re: [PATCH V3 04/20] nvdimm/label: Update mutex_lock() with
 guard(mutex)()



On 9/17/25 6:41 AM, Neeraj Kumar wrote:
> Updated mutex_lock() with guard(mutex)()

Need a bit more in the commit log on why the change so whomever reads the commit later on has an idea what is happening. 
> 
> Signed-off-by: Neeraj Kumar <s.neeraj@...sung.com>
> ---
>  drivers/nvdimm/label.c | 36 +++++++++++++++++-------------------
>  1 file changed, 17 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/nvdimm/label.c b/drivers/nvdimm/label.c
> index 668e1e146229..3235562d0e1c 100644
> --- a/drivers/nvdimm/label.c
> +++ b/drivers/nvdimm/label.c
> @@ -948,7 +948,7 @@ static int __pmem_label_update(struct nd_region *nd_region,
>  		return rc;
>  
>  	/* Garbage collect the previous label */
> -	mutex_lock(&nd_mapping->lock);
> +	guard(mutex)(&nd_mapping->lock);
>  	list_for_each_entry(label_ent, &nd_mapping->labels, list) {
>  		if (!label_ent->label)
>  			continue;
> @@ -960,20 +960,20 @@ static int __pmem_label_update(struct nd_region *nd_region,
>  	/* update index */
>  	rc = nd_label_write_index(ndd, ndd->ns_next,
>  			nd_inc_seq(__le32_to_cpu(nsindex->seq)), 0);
> -	if (rc == 0) {
> -		list_for_each_entry(label_ent, &nd_mapping->labels, list)
> -			if (!label_ent->label) {
> -				label_ent->label = nd_label;
> -				nd_label = NULL;
> -				break;
> -			}
> -		dev_WARN_ONCE(&nspm->nsio.common.dev, nd_label,
> -				"failed to track label: %d\n",
> -				to_slot(ndd, nd_label));
> -		if (nd_label)
> -			rc = -ENXIO;
> -	}
> -	mutex_unlock(&nd_mapping->lock);
> +	if (rc)
> +		return rc;
> +
> +	list_for_each_entry(label_ent, &nd_mapping->labels, list)
> +		if (!label_ent->label) {
> +			label_ent->label = nd_label;
> +			nd_label = NULL;
> +			break;
> +		}
> +	dev_WARN_ONCE(&nspm->nsio.common.dev, nd_label,
> +			"failed to track label: %d\n",
> +			to_slot(ndd, nd_label));
> +	if (nd_label)
> +		rc = -ENXIO;
>  
>  	return rc;
>  }
> @@ -998,9 +998,8 @@ static int init_labels(struct nd_mapping *nd_mapping, int num_labels)
>  		label_ent = kzalloc(sizeof(*label_ent), GFP_KERNEL);
>  		if (!label_ent)
>  			return -ENOMEM;
> -		mutex_lock(&nd_mapping->lock);
> +		guard(mutex)(&nd_mapping->lock);
>  		list_add_tail(&label_ent->list, &nd_mapping->labels);
> -		mutex_unlock(&nd_mapping->lock);

I would not mix and match old and new locking flow in a function. If you are going to convert, then do the whole function. I think earlier in this function you may need a scoped_guard() call.

>  	}
>  
>  	if (ndd->ns_current == -1 || ndd->ns_next == -1)
> @@ -1039,7 +1038,7 @@ static int del_labels(struct nd_mapping *nd_mapping, uuid_t *uuid)
>  	if (!preamble_next(ndd, &nsindex, &free, &nslot))
>  		return 0;
>  
> -	mutex_lock(&nd_mapping->lock);
> +	guard(mutex)(&nd_mapping->lock);

So this change now includes nd_label_write_index() in the lock context as well compare to the old code. So either you should use a scoped_guard() or create a helper function and move the block of code being locked to the helper function with guard() to avoid changing the original code flow.

DJ

>  	list_for_each_entry_safe(label_ent, e, &nd_mapping->labels, list) {
>  		struct nd_namespace_label *nd_label = label_ent->label;
>  
> @@ -1061,7 +1060,6 @@ static int del_labels(struct nd_mapping *nd_mapping, uuid_t *uuid)
>  		nd_mapping_free_labels(nd_mapping);
>  		dev_dbg(ndd->dev, "no more active labels\n");
>  	}
> -	mutex_unlock(&nd_mapping->lock);
>  
>  	return nd_label_write_index(ndd, ndd->ns_next,
>  			nd_inc_seq(__le32_to_cpu(nsindex->seq)), 0);