Commit a4533cc0 authored by Neeraj Upadhyay's avatar Neeraj Upadhyay Committed by Joel Fernandes (Google)
Browse files

rcu-tasks: Report stalls during synchronize_srcu() in rcu_tasks_postscan() 



The call to synchronize_srcu() from rcu_tasks_postscan() can be stalled
by a task getting stuck in do_exit() between that function's calls to
exit_tasks_rcu_start() and exit_tasks_rcu_finish().   To ease diagnosis
of this situation, print a stall warning message every rcu_task_stall_info
period when rcu_tasks_postscan() is stalled.

[ paulmck: Adjust to handle CONFIG_SMP=n. ]

Acked-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Reported-by: default avatarMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/rcu/20230111212736.GA1062057@paulmck-ThinkPad-P17-Gen-1/


Signed-off-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
parent 7ea91307

kernel/rcu/tasks.h

+31 −0
Original line number Diff line number Diff line
@@ -139,6 +139,12 @@ static struct rcu_tasks rt_name = \ 
/* Track exiting tasks in order to allow them to be waited for. */

DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);



#ifdef CONFIG_TASKS_RCU

/* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */

static void tasks_rcu_exit_srcu_stall(struct timer_list *unused);

static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall);

#endif



/* Avoid IPIing CPUs early in the grace period. */

#define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0)

static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY;
@@ -830,6 +836,13 @@ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) 
/* Processing between scanning taskslist and draining the holdout list. */

static void rcu_tasks_postscan(struct list_head *hop)

{

	int rtsi = READ_ONCE(rcu_task_stall_info);



	if (!IS_ENABLED(CONFIG_TINY_RCU)) {

		tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi;

		add_timer(&tasks_rcu_exit_srcu_stall_timer);

	}



	/*

	 * Exiting tasks may escape the tasklist scan. Those are vulnerable

	 * until their final schedule() with TASK_DEAD state. To cope with
@@ -848,6 +861,9 @@ static void rcu_tasks_postscan(struct list_head *hop) 
	 * call to synchronize_rcu().

	 */

	synchronize_srcu(&tasks_rcu_exit_srcu);



	if (!IS_ENABLED(CONFIG_TINY_RCU))

		del_timer_sync(&tasks_rcu_exit_srcu_stall_timer);

}



/* See if tasks are still holding out, complain if so. */
@@ -923,6 +939,21 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp) 
void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);

DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");



static void tasks_rcu_exit_srcu_stall(struct timer_list *unused)

{

#ifndef CONFIG_TINY_RCU

	int rtsi;



	rtsi = READ_ONCE(rcu_task_stall_info);

	pr_info("%s: %s grace period number %lu (since boot) gp_state: %s is %lu jiffies old.\n",

		__func__, rcu_tasks.kname, rcu_tasks.tasks_gp_seq,

		tasks_gp_state_getname(&rcu_tasks), jiffies - rcu_tasks.gp_jiffies);

	pr_info("Please check any exiting tasks stuck between calls to exit_tasks_rcu_start() and exit_tasks_rcu_finish()\n");

	tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi;

	add_timer(&tasks_rcu_exit_srcu_stall_timer);

#endif // #ifndef CONFIG_TINY_RCU

}



/**

 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period

 * @rhp: structure to be used for queueing the RCU updates.