[PATCH] rcu: Finish folding ->fqs_state into ->gp_state

From: Paul E. McKenney
Date: Fri Sep 04 2015 - 19:24:22 EST


Commit commit 4cdfc175c25c89ee ("rcu: Move quiescent-state forcing
into kthread") started the process of folding the old ->fqs_state
into ->gp_state, but did not complete it. This situation does not
cause any malfunction, but can result in extremely confusing trace
output. This commit completes this task of eliminating ->fqs_state
in favor of ->gp_state.

The old fqs_state had one side effect. It was used to decide whether
to collect dyntick-idle snapshots. For this purpose, we add a boolean
into the state struct.

Reported-by: Petr Mladek <pmladek@xxxxxxxx>
Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
---
kernel/rcu/tree.c | 17 +++++++----------
kernel/rcu/tree.h | 16 +++++-----------
kernel/rcu/tree_trace.c | 2 +-
3 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9f75f25cc5d9..f47067fdc783 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -98,7 +98,7 @@ struct rcu_state sname##_state = { \
.level = { &sname##_state.node[0] }, \
.rda = &sname##_data, \
.call = cr, \
- .fqs_state = RCU_GP_IDLE, \
+ .gp_state = RCU_GP_IDLE, \
.gpnum = 0UL - 300UL, \
.completed = 0UL - 300UL, \
.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
@@ -1927,16 +1927,15 @@ static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
/*
* Do one round of quiescent-state forcing.
*/
-static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
+static void rcu_gp_fqs(struct rcu_state *rsp)
{
- int fqs_state = fqs_state_in;
bool isidle = false;
unsigned long maxj;
struct rcu_node *rnp = rcu_get_root(rsp);

WRITE_ONCE(rsp->gp_activity, jiffies);
rsp->n_force_qs++;
- if (fqs_state == RCU_SAVE_DYNTICK) {
+ if (rsp->save_dyntick) {
/* Collect dyntick-idle snapshots. */
if (is_sysidle_rcu_state(rsp)) {
isidle = true;
@@ -1945,7 +1944,7 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
force_qs_rnp(rsp, dyntick_save_progress_counter,
&isidle, &maxj);
rcu_sysidle_report_gp(rsp, isidle, maxj);
- fqs_state = RCU_FORCE_QS;
+ rsp->save_dyntick = false;
} else {
/* Handle dyntick-idle and offline CPUs. */
isidle = true;
@@ -1959,7 +1958,6 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq(&rnp->lock);
}
- return fqs_state;
}

/*
@@ -2023,7 +2021,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
/* Declare grace period done. */
WRITE_ONCE(rsp->completed, rsp->gpnum);
trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
- rsp->fqs_state = RCU_GP_IDLE;
+ rsp->gp_state = RCU_GP_IDLE;
rdp = this_cpu_ptr(rsp->rda);
/* Advance CBs to reduce false positives below. */
needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
@@ -2041,7 +2039,6 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
*/
static int __noreturn rcu_gp_kthread(void *arg)
{
- int fqs_state;
int gf;
unsigned long j;
int ret;
@@ -2073,7 +2070,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
}

/* Handle quiescent-state forcing. */
- fqs_state = RCU_SAVE_DYNTICK;
+ rsp->save_dyntick = true;
j = jiffies_till_first_fqs;
if (j > HZ) {
j = HZ;
@@ -2101,7 +2098,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsstart"));
- fqs_state = rcu_gp_fqs(rsp, fqs_state);
+ rcu_gp_fqs(rsp);
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsend"));
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 2e991f8361e4..12303ff25077 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -412,13 +412,6 @@ struct rcu_data {
struct rcu_state *rsp;
};

-/* Values for fqs_state field in struct rcu_state. */
-#define RCU_GP_IDLE 0 /* No grace period in progress. */
-#define RCU_GP_INIT 1 /* Grace period being initialized. */
-#define RCU_SAVE_DYNTICK 2 /* Need to scan dyntick state. */
-#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
-#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
-
/* Values for nocb_defer_wakeup field in struct rcu_data. */
#define RCU_NOGP_WAKE_NOT 0
#define RCU_NOGP_WAKE 1
@@ -469,15 +462,16 @@ struct rcu_state {

/* The following fields are guarded by the root rcu_node's lock. */

- u8 fqs_state ____cacheline_internodealigned_in_smp;
- /* Force QS state. */
- u8 boost; /* Subject to priority boost. */
+ u8 boost ____cacheline_internodealigned_in_smp;
+ /* Subject to priority boost. */
unsigned long gpnum; /* Current gp number. */
unsigned long completed; /* # of last completed gp. */
struct task_struct *gp_kthread; /* Task for grace periods. */
wait_queue_head_t gp_wq; /* Where GP task waits. */
short gp_flags; /* Commands for GP task. */
short gp_state; /* GP kthread sleep state. */
+ bool save_dyntick; /* Collect dyntick-idle */
+ /* snapshots when forcing QS. */

/* End of fields guarded by root rcu_node's lock. */

@@ -539,7 +533,7 @@ struct rcu_state {
#define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */

/* Values for rcu_state structure's gp_flags field. */
-#define RCU_GP_WAIT_INIT 0 /* Initial state. */
+#define RCU_GP_IDLE 0 /* Initial state and no GP in progress. */
#define RCU_GP_WAIT_GPS 1 /* Wait for grace-period start. */
#define RCU_GP_DONE_GPS 2 /* Wait done for grace-period start. */
#define RCU_GP_WAIT_FQS 3 /* Wait for force-quiescent-state time. */
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index 6fc4c5ff3bb5..1d61f5ba4641 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -268,7 +268,7 @@ static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
gpnum = rsp->gpnum;
seq_printf(m, "c=%ld g=%ld s=%d jfq=%ld j=%x ",
ulong2long(rsp->completed), ulong2long(gpnum),
- rsp->fqs_state,
+ rsp->gp_state,
(long)(rsp->jiffies_force_qs - jiffies),
(int)(jiffies & 0xffff));
seq_printf(m, "nfqs=%lu/nfqsng=%lu(%lu) fqlh=%lu oqlen=%ld/%ld\n",
--
1.8.5.6


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