rcu: Finish folding ->fqs_state into ->gp_state

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 was also used to decide when to collect dyntick-idle
snapshots.  For this purpose, we add a boolean variable into the kthread,
which is set on the first call to rcu_gp_fqs() for a given grace period
and clear otherwise.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 713eb92314b43ec2e98c888223bd80a60fef5fe4..4d296b0fb987f4408ea25db031c39306e6f0b1bf 100644 (file)
--- 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), \
@@ -1936,16 +1936,15 @@ 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, bool first_time)
 {
-       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 (first_time) {
                /* Collect dyntick-idle snapshots. */
                if (is_sysidle_rcu_state(rsp)) {
                        isidle = true;
@@ -1954,7 +1953,6 @@ 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;
        } else {
                /* Handle dyntick-idle and offline CPUs. */
                isidle = true;
@@ -1968,7 +1966,6 @@ 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;
 }
 
 /*
@@ -2032,7 +2029,7 @@ 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;
@@ -2050,7 +2047,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
  */
 static int __noreturn rcu_gp_kthread(void *arg)
 {
-       int fqs_state;
+       bool first_gp_fqs;
        int gf;
        unsigned long j;
        int ret;
@@ -2082,7 +2079,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
                }
 
                /* Handle quiescent-state forcing. */
-               fqs_state = RCU_SAVE_DYNTICK;
+               first_gp_fqs = true;
                j = jiffies_till_first_fqs;
                if (j > HZ) {
                        j = HZ;
@@ -2110,7 +2107,8 @@ 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, first_gp_fqs);
+                               first_gp_fqs = false;
                                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 0c33c82cec643ddba18dc2894f034c7af48aaad6..be6d1e8eeb79ed476c493589abd15a4ed2ab9ca9 100644 (file)
--- 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
@@ -468,9 +461,8 @@ 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. */
@@ -538,7 +530,7 @@ 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 6fc4c5ff3bb5cf55925a1da6ba73d269d3349d49..1d61f5ba4641c42dc4b0dab491acf6f3e5059324 100644 (file)
--- 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",