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authorPeter Zijlstra <peterz@infradead.org>2016-09-13 18:37:29 +0200
committerIngo Molnar <mingo@kernel.org>2016-09-22 14:53:45 +0200
commit9af6528ee9b682df7f29dbee86fbba0b67eab944 (patch)
tree4c4d95d0ab025f7d7120694718670efce57488b2 /kernel/exit.c
parentbf89a304722f6904009499a31dc68ab9a5c9742e (diff)
sched/core: Optimize __schedule()
Oleg noted that by making do_exit() use __schedule() for the TASK_DEAD context switch, we can avoid the TASK_DEAD special case currently in __schedule() because that avoids the extra preempt_disable() from schedule(). In order to facilitate this, create a do_task_dead() helper which we place in the scheduler code, such that it can access __schedule(). Also add some __noreturn annotations to the functions, there's no coming back from do_exit(). Suggested-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Cheng Chao <cs.os.kernel@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: akpm@linux-foundation.org Cc: chris@chris-wilson.co.uk Cc: tj@kernel.org Link: http://lkml.kernel.org/r/20160913163729.GB5012@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/exit.c')
-rw-r--r--kernel/exit.c26
1 files changed, 2 insertions, 24 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 091a78be3b09..1e1d913914c0 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -725,7 +725,7 @@ static void check_stack_usage(void)
static inline void check_stack_usage(void) {}
#endif
-void do_exit(long code)
+void __noreturn do_exit(long code)
{
struct task_struct *tsk = current;
int group_dead;
@@ -882,29 +882,7 @@ void do_exit(long code)
exit_rcu();
TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
- /*
- * The setting of TASK_RUNNING by try_to_wake_up() may be delayed
- * when the following two conditions become true.
- * - There is race condition of mmap_sem (It is acquired by
- * exit_mm()), and
- * - SMI occurs before setting TASK_RUNINNG.
- * (or hypervisor of virtual machine switches to other guest)
- * As a result, we may become TASK_RUNNING after becoming TASK_DEAD
- *
- * To avoid it, we have to wait for releasing tsk->pi_lock which
- * is held by try_to_wake_up()
- */
- smp_mb();
- raw_spin_unlock_wait(&tsk->pi_lock);
-
- /* causes final put_task_struct in finish_task_switch(). */
- tsk->state = TASK_DEAD;
- tsk->flags |= PF_NOFREEZE; /* tell freezer to ignore us */
- schedule();
- BUG();
- /* Avoid "noreturn function does return". */
- for (;;)
- cpu_relax(); /* For when BUG is null */
+ do_task_dead();
}
EXPORT_SYMBOL_GPL(do_exit);