[PATCH] kdump: Add missing RAM resource in crash_shrink_memory()

[Michael Holzheu]

From: Michael Holzheu <holzheu at linux.vnet.ibm.com>

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 at linux.vnet.ibm.com>
---
 kernel/kexec.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1132,6 +1132,7 @@ int crash_shrink_memory(unsigned long ne
 {
 	int ret = 0;
 	unsigned long start, end;
+	struct resource *ram_res;
 
 	mutex_lock(&kexec_mutex);
 
@@ -1149,6 +1150,12 @@ int crash_shrink_memory(unsigned long ne
 		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);
 
@@ -1157,7 +1164,15 @@ int crash_shrink_memory(unsigned long ne
 
 	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: