cxl/region: Recycle region ids

[ Upstream commit 8f401ec1c8975eabfe4c089de91cbe058deabf71 ]

At region creation time the next region-id is atomically cached so that
there is predictability of region device names. If that region is
destroyed and then a new one is created the region id increments. That
ends up looking like a memory leak, or is otherwise surprising that
identifiers roll forward even after destroying all previously created
regions.

Try to reuse rather than free old region ids at region release time.

While this fixes a cosmetic issue, the needlessly advancing memory
region-id gives the appearance of a memory leak, hence the "Fixes" tag,
but no "Cc: stable" tag.

Cc: Ben Widawsky <bwidawsk@kernel.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Fixes: 779dd20cfb56 ("cxl/region: Add region creation support")
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lore.kernel.org/r/166752186062.947915.13200195701224993317.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 6b7fb955a05ac1344d0ef299f69a91fe5e9ae236..78344e4d4215bf0dbfd3dacf876f09380ebef42e 100644 (file)
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -1533,9 +1533,24 @@ static const struct attribute_group *region_groups[] = {
 
 static void cxl_region_release(struct device *dev)
 {
+       struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev->parent);
        struct cxl_region *cxlr = to_cxl_region(dev);
+       int id = atomic_read(&cxlrd->region_id);
+
+       /*
+        * Try to reuse the recently idled id rather than the cached
+        * next id to prevent the region id space from increasing
+        * unnecessarily.
+        */
+       if (cxlr->id < id)
+               if (atomic_try_cmpxchg(&cxlrd->region_id, &id, cxlr->id)) {
+                       memregion_free(id);
+                       goto out;
+               }
 
        memregion_free(cxlr->id);
+out:
+       put_device(dev->parent);
        kfree(cxlr);
 }
 
@@ -1597,6 +1612,11 @@ static struct cxl_region *cxl_region_alloc(struct cxl_root_decoder *cxlrd, int i
        device_initialize(dev);
        lockdep_set_class(&dev->mutex, &cxl_region_key);
        dev->parent = &cxlrd->cxlsd.cxld.dev;
+       /*
+        * Keep root decoder pinned through cxl_region_release to fixup
+        * region id allocations
+        */
+       get_device(dev->parent);
        device_set_pm_not_required(dev);
        dev->bus = &cxl_bus_type;
        dev->type = &cxl_region_type;