rcu: Eliminate stall-warning use of rsp

Now that there is only one rcu_state structure, there is less point
in maintaining a pointer to it.  This commit therefore replaces rsp
with &rcu_state in print_other_cpu_stall(), print_cpu_stall(), and
check_cpu_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4c920e2..2f6fd07 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1273,17 +1273,17 @@ static void rcu_dump_cpu_stacks(void)
 static void rcu_stall_kick_kthreads(void)
 {
        unsigned long j;
-       struct rcu_state *rsp = &rcu_state;
 
        if (!rcu_kick_kthreads)
                return;
-       j = READ_ONCE(rsp->jiffies_kick_kthreads);
-       if (time_after(jiffies, j) && rsp->gp_kthread &&
-           (rcu_gp_in_progress() || READ_ONCE(rsp->gp_flags))) {
-               WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
+       j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
+       if (time_after(jiffies, j) && rcu_state.gp_kthread &&
+           (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
+               WARN_ONCE(1, "Kicking %s grace-period kthread\n",
+                         rcu_state.name);
                rcu_ftrace_dump(DUMP_ALL);
-               wake_up_process(rsp->gp_kthread);
-               WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
+               wake_up_process(rcu_state.gp_kthread);
+               WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
        }
 }
 
@@ -1301,7 +1301,6 @@ static void print_other_cpu_stall(unsigned long gp_seq)
        unsigned long j;
        int ndetected = 0;
        struct rcu_node *rnp = rcu_get_root();
-       struct rcu_state *rsp = &rcu_state;
        long totqlen = 0;
 
        /* Kick and suppress, if so configured. */
@@ -1314,7 +1313,7 @@ static void print_other_cpu_stall(unsigned long gp_seq)
         * See Documentation/RCU/stallwarn.txt for info on how to debug
         * RCU CPU stall warnings.
         */
-       pr_err("INFO: %s detected stalls on CPUs/tasks:", rsp->name);
+       pr_err("INFO: %s detected stalls on CPUs/tasks:", rcu_state.name);
        print_cpu_stall_info_begin();
        rcu_for_each_leaf_node(rnp) {
                raw_spin_lock_irqsave_rcu_node(rnp, flags);
@@ -1334,21 +1333,21 @@ static void print_other_cpu_stall(unsigned long gp_seq)
                totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(&rcu_data,
                                                            cpu)->cblist);
        pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
-              smp_processor_id(), (long)(jiffies - rsp->gp_start),
-              (long)rcu_seq_current(&rsp->gp_seq), totqlen);
+              smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
+              (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
        if (ndetected) {
                rcu_dump_cpu_stacks();
 
                /* Complain about tasks blocking the grace period. */
                rcu_print_detail_task_stall();
        } else {
-               if (rcu_seq_current(&rsp->gp_seq) != gp_seq) {
+               if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
                        pr_err("INFO: Stall ended before state dump start\n");
                } else {
                        j = jiffies;
-                       gpa = READ_ONCE(rsp->gp_activity);
+                       gpa = READ_ONCE(rcu_state.gp_activity);
                        pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
-                              rsp->name, j - gpa, j, gpa,
+                              rcu_state.name, j - gpa, j, gpa,
                               jiffies_till_next_fqs,
                               rcu_get_root()->qsmask);
                        /* In this case, the current CPU might be at fault. */
@@ -1356,8 +1355,8 @@ static void print_other_cpu_stall(unsigned long gp_seq)
                }
        }
        /* Rewrite if needed in case of slow consoles. */
-       if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
-               WRITE_ONCE(rsp->jiffies_stall,
+       if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
+               WRITE_ONCE(rcu_state.jiffies_stall,
                           jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
 
        rcu_check_gp_kthread_starvation();
@@ -1373,7 +1372,6 @@ static void print_cpu_stall(void)
        unsigned long flags;
        struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
        struct rcu_node *rnp = rcu_get_root();
-       struct rcu_state *rsp = &rcu_state;
        long totqlen = 0;
 
        /* Kick and suppress, if so configured. */
@@ -1386,7 +1384,7 @@ static void print_cpu_stall(void)
         * See Documentation/RCU/stallwarn.txt for info on how to debug
         * RCU CPU stall warnings.
         */
-       pr_err("INFO: %s self-detected stall on CPU", rsp->name);
+       pr_err("INFO: %s self-detected stall on CPU", rcu_state.name);
        print_cpu_stall_info_begin();
        raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
        print_cpu_stall_info(smp_processor_id());
@@ -1396,8 +1394,8 @@ static void print_cpu_stall(void)
                totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(&rcu_data,
                                                            cpu)->cblist);
        pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n",
-               jiffies - rsp->gp_start,
-               (long)rcu_seq_current(&rsp->gp_seq), totqlen);
+               jiffies - rcu_state.gp_start,
+               (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
 
        rcu_check_gp_kthread_starvation();
 
@@ -1405,8 +1403,8 @@ static void print_cpu_stall(void)
 
        raw_spin_lock_irqsave_rcu_node(rnp, flags);
        /* Rewrite if needed in case of slow consoles. */
-       if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
-               WRITE_ONCE(rsp->jiffies_stall,
+       if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
+               WRITE_ONCE(rcu_state.jiffies_stall,
                           jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
        raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
@@ -1431,7 +1429,6 @@ static void check_cpu_stall(struct rcu_data *rdp)
        unsigned long jn;
        unsigned long js;
        struct rcu_node *rnp;
-       struct rcu_state *rsp = &rcu_state;
 
        if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
            !rcu_gp_in_progress())
@@ -1442,27 +1439,28 @@ static void check_cpu_stall(struct rcu_data *rdp)
        /*
         * Lots of memory barriers to reject false positives.
         *
-        * The idea is to pick up rsp->gp_seq, then rsp->jiffies_stall,
-        * then rsp->gp_start, and finally another copy of rsp->gp_seq.
-        * These values are updated in the opposite order with memory
-        * barriers (or equivalent) during grace-period initialization
-        * and cleanup.  Now, a false positive can occur if we get an new
-        * value of rsp->gp_start and a old value of rsp->jiffies_stall.
-        * But given the memory barriers, the only way that this can happen
-        * is if one grace period ends and another starts between these
-        * two fetches.  This is detected by comparing the second fetch
-        * of rsp->gp_seq with the previous fetch from rsp->gp_seq.
+        * The idea is to pick up rcu_state.gp_seq, then
+        * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
+        * another copy of rcu_state.gp_seq.  These values are updated in
+        * the opposite order with memory barriers (or equivalent) during
+        * grace-period initialization and cleanup.  Now, a false positive
+        * can occur if we get an new value of rcu_state.gp_start and a old
+        * value of rcu_state.jiffies_stall.  But given the memory barriers,
+        * the only way that this can happen is if one grace period ends
+        * and another starts between these two fetches.  This is detected
+        * by comparing the second fetch of rcu_state.gp_seq with the
+        * previous fetch from rcu_state.gp_seq.
         *
-        * Given this check, comparisons of jiffies, rsp->jiffies_stall,
-        * and rsp->gp_start suffice to forestall false positives.
+        * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
+        * and rcu_state.gp_start suffice to forestall false positives.
         */
-       gs1 = READ_ONCE(rsp->gp_seq);
+       gs1 = READ_ONCE(rcu_state.gp_seq);
        smp_rmb(); /* Pick up ->gp_seq first... */
-       js = READ_ONCE(rsp->jiffies_stall);
+       js = READ_ONCE(rcu_state.jiffies_stall);
        smp_rmb(); /* ...then ->jiffies_stall before the rest... */
-       gps = READ_ONCE(rsp->gp_start);
+       gps = READ_ONCE(rcu_state.gp_start);
        smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
-       gs2 = READ_ONCE(rsp->gp_seq);
+       gs2 = READ_ONCE(rcu_state.gp_seq);
        if (gs1 != gs2 ||
            ULONG_CMP_LT(j, js) ||
            ULONG_CMP_GE(gps, js))
@@ -1471,14 +1469,14 @@ static void check_cpu_stall(struct rcu_data *rdp)
        jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
        if (rcu_gp_in_progress() &&
            (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
-           cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
+           cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
 
                /* We haven't checked in, so go dump stack. */
                print_cpu_stall();
 
        } else if (rcu_gp_in_progress() &&
                   ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
-                  cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
+                  cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
 
                /* They had a few time units to dump stack, so complain. */
                print_other_cpu_stall(gs2);