kernel/fork.c: virtually mapped stacks: do not disable interrupts

The reason to disable interrupts seems to be to avoid switching to a
different processor while handling per cpu data using individual loads and
stores.  If we use per cpu RMV primitives we will not have to disable
interrupts.

Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1705171055130.5898@east.gentwo.org
Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 11 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 0f69a3e5281e..d2b9d7c31eaf 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -205,19 +205,17 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
         void *stack;
         int i;
 
-        local_irq_disable();
         for (i = 0; i < NR_CACHED_STACKS; i++) {
-                struct vm_struct *s = this_cpu_read(cached_stacks[i]);
+                struct vm_struct *s;
+
+                s = this_cpu_xchg(cached_stacks[i], NULL);
 
                 if (!s)
                         continue;
-                this_cpu_write(cached_stacks[i], NULL);
 
                 tsk->stack_vm_area = s;
-                local_irq_enable();
                 return s->addr;
         }
-        local_irq_enable();
 
         stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE,
                                      VMALLOC_START, VMALLOC_END,
@@ -245,19 +243,15 @@ static inline void free_thread_stack(struct task_struct *tsk)
 {
 #ifdef CONFIG_VMAP_STACK
         if (task_stack_vm_area(tsk)) {
-                unsigned long flags;
                 int i;
 
-                local_irq_save(flags);
                 for (i = 0; i < NR_CACHED_STACKS; i++) {
-                        if (this_cpu_read(cached_stacks[i]))
+                        if (this_cpu_cmpxchg(cached_stacks[i],
+                                        NULL, tsk->stack_vm_area) != NULL)
                                 continue;
 
-                        this_cpu_write(cached_stacks[i], tsk->stack_vm_area);
-                        local_irq_restore(flags);
                         return;
                 }
-                local_irq_restore(flags);
 
                 vfree_atomic(tsk->stack);
                 return;