[PATCH v2] cxl/region: Unregister the pmem region bridge on setup failure

devm_cxl_add_pmem_region() publishes the cxl_pmem_region with device_add()
and only afterwards, under the nvdimm bridge's device lock, arranges for
its removal - and only if the bridge has a driver bound. If it does not,
the function sets -ENXIO and leaves through err_bridge, which drops the
reference this function took on the bridge and returns. The device that
was just added has no owner at that point: no device_del(), no
put_device(), and no devm action to do either later. The sibling failure,
a devm_add_action_or_reset() that cannot allocate, is already covered,
because devm_add_action_or_reset() runs cxlr_pmem_unregister() itself on
that path.

An unbound bridge is a normal state, not an error state. The bridge is
unbound whenever cxl_pmem is unloaded or its device is detached through
sysfs, and a region can be probed in that window.

The added device then stays in sysfs, along with the reference it holds on
the region, until the module is unloaded. cxlr->cxlr_pmem still points at
it, and worse, the name is still taken: a later probe of the same region
allocates a second cxl_pmem_region and fails in device_add() on the
duplicate "pmem_region%d", so once this has happened the region can no
longer be brought up at all.

Call cxlr_pmem_unregister() on that branch. It is invoked from inside the
scoped_guard() that holds the bridge's device lock, which is what its
device_lock_assert() requires, and it performs the same teardown the devm
action would have performed, including clearing cxlr->cxlr_pmem, so
err_bridge is left with only the bridge reference to drop.

Fixes: f17b558d6663 ("cxl/pmem: Refactor nvdimm device registration, delete the workqueue")
Signed-off-by: Guixin Liu <[email protected]>
---
This was patch 8/8 of the "cxl: Assorted fixes" series [1]. Per review
feedback that series is not being reworked as a whole; the fixes are resent
individually instead. Patches 1, 2 and 7 of the series are dropped, as those
issues are already fixed in cxl/next.

v1->v2:
- rebase onto cxl/next
- rewrite the commit message to describe the behaviour rather than narrate
  the code change (Alison Schofield)

[1] https://lore.kernel.org/linux-cxl/[email protected]/

 drivers/cxl/core/region_pmem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/region_pmem.c b/drivers/cxl/core/region_pmem.c
index 23d97e3d78b6..7ab1373a95e0 100644
--- a/drivers/cxl/core/region_pmem.c
+++ b/drivers/cxl/core/region_pmem.c
@@ -168,12 +168,14 @@ int devm_cxl_add_pmem_region(struct cxl_region *cxlr)
 		dev_name(dev));
 
 	scoped_guard(device, &cxl_nvb->dev) {
-		if (cxl_nvb->dev.driver)
+		if (cxl_nvb->dev.driver) {
 			rc = devm_add_action_or_reset(&cxl_nvb->dev,
 						      cxlr_pmem_unregister,
 						      cxlr_pmem);
-		else
+		} else {
 			rc = -ENXIO;
+			cxlr_pmem_unregister(cxlr_pmem);
+		}
 	}
 
 	if (rc)

base-commit: 7098e9cd98a05c0c5de2fae0c2465f9d966fdd07
-- 
2.43.7