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Commit 8c7c4829 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Awaken grace-period kthread if too long since FQS 



Recent kernels can fail to awaken the grace-period kthread for
quiescent-state forcing.  This commit is a crude hack that does
a wakeup if a scheduling-clock interrupt sees that it has been
too long since force-quiescent-state (FQS) processing.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent fcfd0a23

kernel/rcu/tree.c

+37 −2
Original line number Diff line number Diff line
@@ -385,9 +385,11 @@ module_param(qlowmark, long, 0444); 


static ulong jiffies_till_first_fqs = ULONG_MAX;

static ulong jiffies_till_next_fqs = ULONG_MAX;

static bool rcu_kick_kthreads;



module_param(jiffies_till_first_fqs, ulong, 0644);

module_param(jiffies_till_next_fqs, ulong, 0644);

module_param(rcu_kick_kthreads, bool, 0644);



/*

 * How long the grace period must be before we start recruiting
@@ -1251,6 +1253,24 @@ static void rcu_dump_cpu_stacks(struct rcu_state *rsp) 
	}

}



/*

 * If too much time has passed in the current grace period, and if

 * so configured, go kick the relevant kthreads.

 */

static void rcu_stall_kick_kthreads(struct rcu_state *rsp)

{

	unsigned long j;



	if (!rcu_kick_kthreads)

		return;

	j = READ_ONCE(rsp->jiffies_kick_kthreads);

	if (time_after(jiffies, j) && rsp->gp_kthread) {

		WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);

		wake_up_process(rsp->gp_kthread);

		WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);

	}

}



static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)

{

	int cpu;
@@ -1262,6 +1282,11 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum) 
	struct rcu_node *rnp = rcu_get_root(rsp);

	long totqlen = 0;



	/* Kick and suppress, if so configured. */

	rcu_stall_kick_kthreads(rsp);

	if (rcu_cpu_stall_suppress)

		return;



	/* Only let one CPU complain about others per time interval. */



	raw_spin_lock_irqsave_rcu_node(rnp, flags);
@@ -1335,6 +1360,11 @@ static void print_cpu_stall(struct rcu_state *rsp) 
	struct rcu_node *rnp = rcu_get_root(rsp);

	long totqlen = 0;



	/* Kick and suppress, if so configured. */

	rcu_stall_kick_kthreads(rsp);

	if (rcu_cpu_stall_suppress)

		return;



	/*

	 * OK, time to rat on ourselves...

	 * See Documentation/RCU/stallwarn.txt for info on how to debug
@@ -1379,8 +1409,10 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) 
	unsigned long js;

	struct rcu_node *rnp;



	if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))

	if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||

	    !rcu_gp_in_progress(rsp))

		return;

	rcu_stall_kick_kthreads(rsp);

	j = jiffies;



	/*
@@ -2119,8 +2151,11 @@ static int __noreturn rcu_gp_kthread(void *arg) 
		}

		ret = 0;

		for (;;) {

			if (!ret)

			if (!ret) {

				rsp->jiffies_force_qs = jiffies + j;

				WRITE_ONCE(rsp->jiffies_kick_kthreads,

					   jiffies + 3 * j);

			}

			trace_rcu_grace_period(rsp->name,

					       READ_ONCE(rsp->gpnum),

					       TPS("fqswait"));

kernel/rcu/tree.h

+2 −0
Original line number Diff line number Diff line
@@ -513,6 +513,8 @@ struct rcu_state { 


	unsigned long jiffies_force_qs;		/* Time at which to invoke */

						/*  force_quiescent_state(). */

	unsigned long jiffies_kick_kthreads;	/* Time at which to kick */

						/*  kthreads, if configured. */

	unsigned long n_force_qs;		/* Number of calls to */

						/*  force_quiescent_state(). */

	unsigned long n_force_qs_lh;		/* ~Number of calls leaving */