Commit 8eb23b9f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Debug nested sleeps 



Validate we call might_sleep() with TASK_RUNNING, which catches places
where we nest blocking primitives, eg. mutex usage in a wait loop.

Since all blocking is arranged through task_struct::state, nesting
this will cause the inner primitive to set TASK_RUNNING and the outer
will thus not block.

Another observed problem is calling a blocking function from
schedule()->sched_submit_work()->blk_schedule_flush_plug() which will
then destroy the task state for the actual __schedule() call that
comes after it.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: tglx@linutronix.de
Cc: ilya.dryomov@inktank.com
Cc: umgwanakikbuti@gmail.com
Cc: oleg@redhat.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140924082242.591637616@infradead.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 26cabd31

include/linux/sched.h

+44 −2
Original line number Diff line number Diff line
@@ -243,6 +243,43 @@ extern char ___assert_task_state[1 - 2*!!( 
				((task->state & TASK_UNINTERRUPTIBLE) != 0 && \

				 (task->flags & PF_FROZEN) == 0)



#ifdef CONFIG_DEBUG_ATOMIC_SLEEP



#define __set_task_state(tsk, state_value)			\

	do {							\

		(tsk)->task_state_change = _THIS_IP_;		\

		(tsk)->state = (state_value);			\

	} while (0)

#define set_task_state(tsk, state_value)			\

	do {							\

		(tsk)->task_state_change = _THIS_IP_;		\

		set_mb((tsk)->state, (state_value));		\

	} while (0)



/*

 * set_current_state() includes a barrier so that the write of current->state

 * is correctly serialised wrt the caller's subsequent test of whether to

 * actually sleep:

 *

 *	set_current_state(TASK_UNINTERRUPTIBLE);

 *	if (do_i_need_to_sleep())

 *		schedule();

 *

 * If the caller does not need such serialisation then use __set_current_state()

 */

#define __set_current_state(state_value)			\

	do {							\

		current->task_state_change = _THIS_IP_;		\

		current->state = (state_value);			\

	} while (0)

#define set_current_state(state_value)				\

	do {							\

		current->task_state_change = _THIS_IP_;		\

		set_mb(current->state, (state_value));		\

	} while (0)



#else



#define __set_task_state(tsk, state_value)		\

	do { (tsk)->state = (state_value); } while (0)

#define set_task_state(tsk, state_value)		\
@@ -264,6 +301,8 @@ extern char ___assert_task_state[1 - 2*!!( 
#define set_current_state(state_value)			\

	set_mb(current->state, (state_value))



#endif



/* Task command name length */

#define TASK_COMM_LEN 16
@@ -1661,6 +1700,9 @@ struct task_struct { 
	unsigned int	sequential_io;

	unsigned int	sequential_io_avg;

#endif

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP

	unsigned long	task_state_change;

#endif

};



/* Future-safe accessor for struct task_struct's cpus_allowed. */

kernel/sched/core.c

+13 −0
Original line number Diff line number Diff line
@@ -7298,6 +7298,19 @@ void __might_sleep(const char *file, int line, int preempt_offset) 
{

	static unsigned long prev_jiffy;	/* ratelimiting */



	/*

	 * Blocking primitives will set (and therefore destroy) current->state,

	 * since we will exit with TASK_RUNNING make sure we enter with it,

	 * otherwise we will destroy state.

	 */

	if (WARN(current->state != TASK_RUNNING,

			"do not call blocking ops when !TASK_RUNNING; "

			"state=%lx set at [<%p>] %pS\n",

			current->state,

			(void *)current->task_state_change,

			(void *)current->task_state_change))

		__set_current_state(TASK_RUNNING);



	rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */

	if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&

	     !is_idle_task(current)) ||

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