x86: cpu_init(): fix memory leak when using CPU hotplug

Exception stacks are allocated each time a CPU is set online.
But the allocated space is never freed. Thus with one CPU hotplug
offline/online cycle there is a memory leak of 24K (6 pages) for
a CPU.

Fix is to allocate exception stacks only once -- when the CPU is
set online for the first time.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: akpm@linux-foundation.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 13 insertions, 10 deletions

diff --git a/arch/x86/kernel/cpu/common_64.c b/arch/x86/kernel/cpu/common_64.c
index 8396fd7628a..cc6efe86249 100644
--- a/arch/x86/kernel/cpu/common_64.c
+++ b/arch/x86/kernel/cpu/common_64.c
@@ -606,19 +606,22 @@ void __cpuinit cpu_init(void)
         /*
          * set up and load the per-CPU TSS
          */
-        for (v = 0; v < N_EXCEPTION_STACKS; v++) {
+        if (!orig_ist->ist[0]) {
                 static const unsigned int order[N_EXCEPTION_STACKS] = {
-                        [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STACK_ORDER,
-                        [DEBUG_STACK - 1] = DEBUG_STACK_ORDER
+                  [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STACK_ORDER,
+                  [DEBUG_STACK - 1] = DEBUG_STACK_ORDER
                 };
-                if (cpu) {
-                        estacks = (char *)__get_free_pages(GFP_ATOMIC, order[v]);
-                        if (!estacks)
-                                panic("Cannot allocate exception stack %ld %d\n",
-                                      v, cpu);
+                for (v = 0; v < N_EXCEPTION_STACKS; v++) {
+                        if (cpu) {
+                                estacks = (char *)__get_free_pages(GFP_ATOMIC, order[v]);
+                                if (!estacks)
+                                        panic("Cannot allocate exception "
+                                              "stack %ld %d\n", v, cpu);
+                        }
+                        estacks += PAGE_SIZE << order[v];
+                        orig_ist->ist[v] = t->x86_tss.ist[v] =
+                                        (unsigned long)estacks;
                 }
-                estacks += PAGE_SIZE << order[v];
-                orig_ist->ist[v] = t->x86_tss.ist[v] = (unsigned long)estacks;
         }
 
         t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);