kdump: add missing RAM resource in crash_shrink_memory()

When shrinking crashkernel memory using /sys/kernel/kexec_crash_size for
the newly added memory no RAM resource is created at the moment.

Example:

  $ cat /proc/iomem
  00000000-bfffffff : System RAM
    00000000-005b7ac3 : Kernel code
    005b7ac4-009743bf : Kernel data
    009bb000-00a85c33 : Kernel bss
  c0000000-cfffffff : Crash kernel
  d0000000-ffffffff : System RAM

  $ echo 0 > /sys/kernel/kexec_crash_size
  $ cat /proc/iomem
  00000000-bfffffff : System RAM
    00000000-005b7ac3 : Kernel code
    005b7ac4-009743bf : Kernel data
    009bb000-00a85c33 : Kernel bss
                                   <<-- here is System RAM missing
  d0000000-ffffffff : System RAM

One result of this bug is that the memory chunk can never be set offline
using memory hotplug.  With this patch I insert a new "System RAM"
resource for the released memory.  Then the upper example looks like the
following:

  $ echo 0 > /sys/kernel/kexec_crash_size
  $ cat /proc/iomem
  00000000-bfffffff : System RAM
    00000000-005b7ac3 : Kernel code
    005b7ac4-009743bf : Kernel data
    009bb000-00a85c33 : Kernel bss
  c0000000-cfffffff : System RAM   <<-- new rescoure
  d0000000-ffffffff : System RAM

And now I can set chunk c0000000-cfffffff offline.
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kexec.c

@@ -1129,6 +1129,7 @@ int crash_shrink_memory(unsigned long new_size)
 {
 	int ret = 0;
 	unsigned long start, end;
+	struct resource *ram_res;
 
 	mutex_lock(&kexec_mutex);
 
@@ -1146,6 +1147,12 @@ int crash_shrink_memory(unsigned long new_size)
 		goto unlock;
 	}
 
+	ram_res = kzalloc(sizeof(*ram_res), GFP_KERNEL);
+	if (!ram_res) {
+		ret = -ENOMEM;
+		goto unlock;
+	}
+
 	start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
 	end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);
 
@@ -1154,7 +1161,15 @@ int crash_shrink_memory(unsigned long new_size)
 
 	if ((start == end) && (crashk_res.parent != NULL))
 		release_resource(&crashk_res);
+
+	ram_res->start = end;
+	ram_res->end = crashk_res.end;
+	ram_res->flags = IORESOURCE_BUSY | IORESOURCE_MEM;
+	ram_res->name = "System RAM";
+
 	crashk_res.end = end - 1;
+
+	insert_resource(&iomem_resource, ram_res);
 	crash_unmap_reserved_pages();
 
 unlock: