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Subject[PATCH 4.12 182/196] kernel/fork.c: virtually mapped stacks: do not disable interrupts
Date
4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Lameter <cl@linux.com>

commit 112166f88cf83dd11486cf1818672d42b540865b upstream.

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>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/fork.c | 16 +++++-----------
1 file changed, 5 insertions(+), 11 deletions(-)

--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -205,19 +205,17 @@ static unsigned long *alloc_thread_stack
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(str
{
#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;

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