diff options
| -rw-r--r-- | kernel/sched/idle.c | 26 |
1 files changed, 25 insertions, 1 deletions
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 25b9423..fe4b24b 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -67,6 +67,10 @@ void __weak arch_cpu_idle(void) * cpuidle_idle_call - the main idle function * * NOTE: no locks or semaphores should be used here + * + * On archs that support TIF_POLLING_NRFLAG, is called with polling + * set, and it returns with polling set. If it ever stops polling, it + * must clear the polling bit. */ static void cpuidle_idle_call(void) { @@ -175,10 +179,22 @@ exit_idle: /* * Generic idle loop implementation + * + * Called with polling cleared. */ static void cpu_idle_loop(void) { while (1) { + /* + * If the arch has a polling bit, we maintain an invariant: + * + * Our polling bit is clear if we're not scheduled (i.e. if + * rq->curr != rq->idle). This means that, if rq->idle has + * the polling bit set, then setting need_resched is + * guaranteed to cause the cpu to reschedule. + */ + + __current_set_polling(); tick_nohz_idle_enter(); while (!need_resched()) { @@ -218,6 +234,15 @@ static void cpu_idle_loop(void) */ preempt_set_need_resched(); tick_nohz_idle_exit(); + __current_clr_polling(); + + /* + * We promise to reschedule if need_resched is set while + * polling is set. That means that clearing polling + * needs to be visible before rescheduling. + */ + smp_mb__after_atomic(); + schedule_preempt_disabled(); } } @@ -239,7 +264,6 @@ void cpu_startup_entry(enum cpuhp_state state) */ boot_init_stack_canary(); #endif - __current_set_polling(); arch_cpu_idle_prepare(); cpu_idle_loop(); } |
