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

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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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2016-01-03 20:29:57 -08:00
parent fcfd0a237b
commit 8c7c4829a8
2 changed files with 39 additions and 2 deletions
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39
kernel/rcu/tree.c
View File

@ -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"));

2
kernel/rcu/tree.h
View File

@ -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 */