[PATCH rcu 07/18] rcutorture: Check preemption for failing reader

[Paul E. McKenney]

This commit checks to see if the RCU reader has been preempted within
its read-side critical section for RCU flavors supporting this notion
(currently only preemptible RCU).  If such a preemption occurred, then
this is printed at the end of the "Failure/close-call rcutorture reader
segments" list at the end of the rcutorture run.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paul...@kernel.org>
Cc: Frederic Weisbecker <frede...@kernel.org>
Tested-by: kernel test robot <oliver.s...@intel.com>
---
 include/linux/rcupdate_wait.h | 11 +++++++++++
 kernel/rcu/rcutorture.c       | 11 +++++++++++
 2 files changed, 22 insertions(+)

diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
index 303ab9bee1552..f9bed3d3f78d9 100644
--- a/include/linux/rcupdate_wait.h
+++ b/include/linux/rcupdate_wait.h
@@ -65,4 +65,15 @@ static inline void cond_resched_rcu(void)
 #endif
 }
 
+// Has the current task blocked within its current RCU read-side
+// critical section?
+static inline bool has_rcu_reader_blocked(void)
+{
+#ifdef CONFIG_PREEMPT_RCU
+       return !list_empty(&current->rcu_node_entry);
+#else
+       return false;
+#endif
+}
+
 #endif /* _LINUX_SCHED_RCUPDATE_WAIT_H */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 658ac46581d81..9b81e21c75d18 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -267,6 +267,7 @@ struct rt_read_seg {
 static int err_segs_recorded;
 static struct rt_read_seg err_segs[RCUTORTURE_RDR_MAX_SEGS];
 static int rt_read_nsegs;
+static int rt_read_preempted;
 
 static const char *rcu_torture_writer_state_getname(void)
 {
@@ -394,6 +395,7 @@ struct rcu_torture_ops {
        void (*get_gp_data)(int *flags, unsigned long *gp_seq);
        void (*gp_slow_register)(atomic_t *rgssp);
        void (*gp_slow_unregister)(atomic_t *rgssp);
+       bool (*reader_blocked)(void);
        long cbflood_max;
        int irq_capable;
        int can_boost;
@@ -587,6 +589,9 @@ static struct rcu_torture_ops rcu_ops = {
        .get_gp_data            = rcutorture_get_gp_data,
        .gp_slow_register       = rcu_gp_slow_register,
        .gp_slow_unregister     = rcu_gp_slow_unregister,
+       .reader_blocked         = IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_CPU)
+                                 ? has_rcu_reader_blocked
+                                 : NULL,
        .irq_capable            = 1,
        .can_boost              = IS_ENABLED(CONFIG_RCU_BOOST),
        .extendables            = RCUTORTURE_MAX_EXTEND,
@@ -2035,6 +2040,7 @@ static bool rcu_torture_one_read(struct 
torture_random_state *trsp, long myid)
        int newstate;
        struct rcu_torture *p;
        int pipe_count;
+       bool preempted = false;
        int readstate = 0;
        struct rt_read_seg rtseg[RCUTORTURE_RDR_MAX_SEGS] = { { 0 } };
        struct rt_read_seg *rtrsp = &rtseg[0];
@@ -2100,6 +2106,8 @@ static bool rcu_torture_one_read(struct 
torture_random_state *trsp, long myid)
                                  rcu_torture_writer_state,
                                  cpumask_pr_args(cpu_online_mask));
        }
+       if (cur_ops->reader_blocked)
+               preempted = cur_ops->reader_blocked();
        rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
        WARN_ON_ONCE(readstate);
        // This next splat is expected behavior if leakpointer, especially
@@ -2112,6 +2120,7 @@ static bool rcu_torture_one_read(struct 
torture_random_state *trsp, long myid)
                for (rtrsp1 = &rtseg[0]; rtrsp1 < rtrsp; rtrsp1++)
                        err_segs[i++] = *rtrsp1;
                rt_read_nsegs = i;
+               rt_read_preempted = preempted;
        }
 
        return true;
@@ -3569,6 +3578,8 @@ rcu_torture_cleanup(void)
                        pr_cont("\n");
 
                }
+               if (rt_read_preempted)
+                       pr_alert("\tReader was preempted.\n");
        }
        if (atomic_read(&n_rcu_torture_error) || n_rcu_torture_barrier_error)
                rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE");
-- 
2.40.1