kexec: add helper __crash_shrink_memory()

No functional change, in preparation for the next patch so that it is easier to review. [akpm@linux-foundation.org: make __crash_shrink_memory() static] Link: https://lore.kernel.org/oe-kbuild-all/202305280717.Pw06aLkz-lkp@intel.com/ Link: https://lkml.kernel.org/r/20230527123439.772-6-thunder.leizhen@huawei.com Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> Acked-by: Baoquan He <bhe@redhat.com> Cc: Cong Wang <amwang@redhat.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Zhen Lei

kernel/kexec_core.c

@@ -1105,11 +1105,38 @@ ssize_t crash_get_memory_size(void)
 return size;
 }
 
+static int __crash_shrink_memory(struct resource *old_res,
+ unsigned long new_size)
+{
+struct resource *ram_res;
+
+ram_res = kzalloc(sizeof(*ram_res), GFP_KERNEL);
+if (!ram_res)
+return -ENOMEM;
+
+ram_res->start = old_res->start + new_size;
+ram_res->end = old_res->end;
+ram_res->flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM;
+ram_res->name = "System RAM";
+
+if (!new_size) {
+release_resource(old_res);
+old_res->start = 0;
+old_res->end = 0;
+} else {
+crashk_res.end = ram_res->start - 1;
+}
+
+crash_free_reserved_phys_range(ram_res->start, ram_res->end);
+insert_resource(&iomem_resource, ram_res);
+
+return 0;
+}
+
 int crash_shrink_memory(unsigned long new_size)
 {
 int ret = 0;
 unsigned long old_size;
-struct resource *ram_res;
 
 if (!kexec_trylock())
 return -EBUSY;
@@ -1125,27 +1152,7 @@ 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;
-}
-
-ram_res->start = crashk_res.start + new_size;
-ram_res->end = crashk_res.end;
-ram_res->flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM;
-ram_res->name = "System RAM";
-
-if (!new_size) {
-release_resource(&crashk_res);
-crashk_res.start = 0;
-crashk_res.end = 0;
-} else {
-crashk_res.end = ram_res->start - 1;
-}
-
-crash_free_reserved_phys_range(ram_res->start, ram_res->end);
-insert_resource(&iomem_resource, ram_res);
+ret = __crash_shrink_memory(&crashk_res, new_size);
 
 unlock:
 kexec_unlock();