rcu: Make RCU_CPU_STALL_INFO include number of fqs attempts

One way that an RCU CPU stall warning can happen is if the grace-period
kthread is not allowed to execute.  One proxy for this kthread's
forward progress is the number of force-quiescent-state (fqs) scans.
This commit therefore adds the number of fqs scans to the RCU CPU stall
warning printouts when CONFIG_RCU_CPU_STALL_INFO=y.

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

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4c106fcc0d54a79d905edf0a6619c77fe2e369e1..654b15be1e365f75b31b7f8dc544e6d0a2a1c480 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1043,6 +1043,7 @@ static void record_gp_stall_check_time(struct rcu_state *rsp)
        j1 = rcu_jiffies_till_stall_check();
        ACCESS_ONCE(rsp->jiffies_stall) = j + j1;
        rsp->jiffies_resched = j + j1 / 2;
+       rsp->n_force_qs_gpstart = ACCESS_ONCE(rsp->n_force_qs);
 }
 
 /*

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 8e7b1843896ebcc0fe13ed51da7cea68f14f0a36..e300848cc0cfab411f6b4d87d243d985df0b1cd5 100644 (file)
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -492,6 +492,8 @@ struct rcu_state {
                                                /*  for CPU stalls. */
        unsigned long jiffies_resched;          /* Time at which to resched */
                                                /*  a reluctant CPU. */
+       unsigned long n_force_qs_gpstart;       /* Snapshot of n_force_qs at */
+                                               /*  GP start. */
        unsigned long gp_max;                   /* Maximum GP duration in */
                                                /*  jiffies. */
        const char *name;                       /* Name of structure. */

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 3ec85cb5d544b8588fd574a80e19bd564079533f..769384d77437891664c69272411ae869e632d0d6 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1898,11 +1898,12 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
                ticks_value = rsp->gpnum - rdp->gpnum;
        }
        print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
-       pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
+       pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
               cpu, ticks_value, ticks_title,
               atomic_read(&rdtp->dynticks) & 0xfff,
               rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
               rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+              ACCESS_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
               fast_no_hz);
 }