大虾留步，“BUG: scheduling while atomic:” 是怎么回事啊？

[olla168]

程序中起了一个线程，有调用wait_event_interruptible()，估计应该是调用schedule时，在schedule打印出来的。

只是这里想不明白if (unlikely(in_atomic() && !current->exit_state)) 这个条件一般什么时候满足？可能是什么原因呢？

从程序上看，那个线程不会在原子上下文运行呢~~ 想不明白啊~~ 大虾指点下啊~~

#define __wait_event_interruptible(wq, condition, ret)			\
do {									\
	DEFINE_WAIT(__wait);						\
									\
	for (;;) {							\
		prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE);	\
		if (condition)						\
			break;						\
		if (!signal_pending(current)) {				\
			schedule();					\
			continue;					\
		}							\
		ret = -ERESTARTSYS;					\
		break;							\
	}								\
	finish_wait(&wq, &__wait);					\
} while (0)

#define wait_event_interruptible(wq, condition)				\
({									\
	int __ret = 0;							\
	if (!(condition))						\
		__wait_event_interruptible(wq, condition, __ret);	\
	__ret;								\
})

asmlinkage void __sched schedule(void)
{
	struct task_struct *prev, *next;
	struct prio_array *array;
	struct list_head *queue;
	unsigned long long now;
	unsigned long run_time;
	int cpu, idx, new_prio;
	long *switch_count;
	struct rq *rq;

	/*
	 * Test if we are atomic.  Since do_exit() needs to call into
	 * schedule() atomically, we ignore that path for now.
	 * Otherwise, whine if we are scheduling when we should not be.
	 */
	if (unlikely(in_atomic() && !current->exit_state)) {
		printk(KERN_ERR "BUG: scheduling while atomic: "
			"%s/0x%08x/%d\n",
			current->comm, preempt_count(), current->pid);
		debug_show_held_locks(current);
		if (irqs_disabled())
			print_irqtrace_events(current);
		dump_stack();
	}
	profile_hit(SCHED_PROFILING, __builtin_return_address(0));

need_resched:
   //...
}

呵呵，本来帖子问题点数想给100分的，可惜只能给60~~ 呵呵，大虾别介意啊~~ 继续指点继续指点~~

[hefuhua]

不是大侠,是老兵

if (unlikely(in_atomic() && !current->exit_state))
我理解是在原子操作中,且当前进程的退出状态为0,那么schedule()是切换进程的,我们知道在原子状态是不能切换进程的,所以这个条件为bug

[olla168]

“当前进程的退出状态为0”是什么意思？

[hefuhua]

Linux/include/linux/sched.h

/*
 * Task state bitmask. NOTE! These bits are also
 * encoded in fs/proc/array.c: get_task_state().
 *
 * We have two separate sets of flags: task->state
 * is about runnability, while task->exit_state are
 * about the task exiting. Confusing, but this way
 * modifying one set can't modify the other one by
 * mistake.
 */
#define TASK_RUNNING            0
#define TASK_INTERRUPTIBLE      1
#define TASK_UNINTERRUPTIBLE    2
#define __TASK_STOPPED          4
#define __TASK_TRACED           8
/* in tsk->exit_state */
#define EXIT_ZOMBIE             16
#define EXIT_DEAD               32
/* in tsk->state again */
#define TASK_DEAD               64
#define TASK_WAKEKILL           128

为0表示TASK_RUNNING状态,也就是说原子状态,而且当前进程在运行,那么就不能切换给其它的进程

[eddiezhou]

遇到同样问题了