Re: [PATCH v6 5/9] dax: Track all dax_region allocations under a global resource tree

Dan Williams
2026-03-12T00:27:47Z

Smita Koralahalli wrote:
> Introduce a global "DAX Regions" resource root and register each
> dax_region->res under it via request_resource(). Release the resource on
> dax_region teardown.
>
> By enforcing a single global namespace for dax_region allocations, this
> ensures only one of dax_hmem or dax_cxl can successfully register a
> dax_region for a given range.
>
> Co-developed-by: Dan Williams <dan.j.williams@intel.com>

Did I send any code for this? If I suggested the locking below,
apologies, otherwise Suggested-by is expected unless code is adopted
from another patch.

> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
> ---
> drivers/dax/bus.c | 23 ++++++++++++++++++++---
> 1 file changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index fde29e0ad68b..5f387feb95f0 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -10,6 +10,7 @@
> #include "dax-private.h"
> #include "bus.h"
>
> +static struct resource dax_regions = DEFINE_RES_MEM_NAMED(0, -1, "DAX Regions");
> static DEFINE_MUTEX(dax_bus_lock);
>
> /*
> @@ -625,6 +626,8 @@ static void dax_region_unregister(void *region)
> {
> struct dax_region *dax_region = region;
>
> + scoped_guard(rwsem_write, &dax_region_rwsem)
> + release_resource(&dax_region->res);

I continue to dislike what scoped_guard() does to indentation. Often
scoped_guard() usage can just be replaced by "helper that uses guard()"

However, dax_region_rwsem protects subdivision of a dax_region, not
coordination across regions.

Also, release_resource() and request_resource() are already protected by
the resource_lock, why is a new lock needed?