Re: [PATCH V3 04/20] nvdimm/label: Update mutex_lock() with guard(mutex)()

Jonathan Cameron
2025-09-17T14:47:01Z

On Wed, 17 Sep 2025 18:59:24 +0530
Neeraj Kumar <s.neeraj@samsung.com> wrote:

> Updated mutex_lock() with guard(mutex)()

Say why.
>
> Signed-off-by: Neeraj Kumar <s.neeraj@samsung.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;

Perhaps it will change in later patches, but you could have done
if (!label_ent->label) {
label_ent->label = nd_label;
return;
}
as nothing else happens if we find a match.

> + }
> + 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);

Not sure I'd bother with cases like this but harmless.

> }
>
> 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);
> 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);
This is a potential functional change as the lock is held for longer than before.
nd_label_write_index is not trivial so reviewing if that is safe is not trivial.

The benefit is small so far (maybe that changes in later patches) so I would not
make the change.

>
> return nd_label_write_index(ndd, ndd->ns_next,
> nd_inc_seq(__le32_to_cpu(nsindex->seq)), 0);