kernel, resource: check for IORESOURCE_SYSRAM in release_mem_region_adjustable

This is a preparation for the next patch.

Currently, we only call release_mem_region_adjustable() in __remove_pages
if the zone is not ZONE_DEVICE, because resources that belong to HMM/devm
are being released by themselves with devm_release_mem_region.

Since we do not want to touch any zone/page stuff during the removing of
the memory (but during the offlining), we do not want to check for the
zone here.  So we need another way to tell release_mem_region_adjustable()
to not realease the resource in case it belongs to HMM/devm.

HMM/devm acquires/releases a resource through
devm_request_mem_region/devm_release_mem_region.

These resources have the flag IORESOURCE_MEM, while resources acquired by
hot-add memory path (register_memory_resource()) contain
IORESOURCE_SYSTEM_RAM.

So, we can check for this flag in release_mem_region_adjustable, and if
the resource does not contain such flag, we know that we are dealing with
a HMM/devm resource, so we can back off.

Link: http://lkml.kernel.org/r/20181127162005.15833-3-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/resource.c b/kernel/resource.c
index b0fbf68..915c02e 100644 (file)
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1256,6 +1256,21 @@ int release_mem_region_adjustable(struct resource *parent,
                        continue;
                }
 
+               /*
+                * All memory regions added from memory-hotplug path have the
+                * flag IORESOURCE_SYSTEM_RAM. If the resource does not have
+                * this flag, we know that we are dealing with a resource coming
+                * from HMM/devm. HMM/devm use another mechanism to add/release
+                * a resource. This goes via devm_request_mem_region and
+                * devm_release_mem_region.
+                * HMM/devm take care to release their resources when they want,
+                * so if we are dealing with them, let us just back off here.
+                */
+               if (!(res->flags & IORESOURCE_SYSRAM)) {
+                       ret = 0;
+                       break;
+               }
+
                if (!(res->flags & IORESOURCE_MEM))
                        break;