rcutorture: Decorate failing reader segments with CPU ID

This commit adds CPU number to the "Failure/close-call rcutorture reader
segments" list printed at the end of an rcutorture run that had too-short
grace periods.  This information can help debugging interactions with
migration and CPU hotplug.

However, experience indicates that sampling the CPU number in rcutorture's
read-side code can reduce the probability of too-short bugs by a small
integer factor.  And small integer factors are crucial to RCU bug hunting,
so this commit also introduces a default-off RCU_TORTURE_TEST_LOG_CPU
Kconfig option to enable this CPU-number-logging functionality at
build time.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 9b0b52e1836fa42b60539edcd33f0c70358b74f2..b3ac000004bfe7f59e41178927cfe2cc9fd32157 100644 (file)
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -53,6 +53,21 @@ config RCU_TORTURE_TEST
          Say M if you want the RCU torture tests to build as a module.
          Say N if you are unsure.
 
+config RCU_TORTURE_TEST_LOG_CPU
+       tristate "Log CPU for rcutorture failures"
+       depends on RCU_TORTURE_TEST
+       default n
+       help
+         This option causes rcutorture to decorate each entry of its
+         log of failure/close-call rcutorture reader segments with the
+         number of the CPU that the reader was running on at the time.
+         This information can be useful, but it does incur additional
+         overhead, overhead that can make both failures and close calls
+         less probable.
+
+         Say Y here if you want CPU IDs logged.
+         Say N if you are unsure.
+
 config RCU_REF_SCALE_TEST
        tristate "Scalability tests for read-side synchronization (RCU and others)"
        depends on DEBUG_KERNEL

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 99780a74da44ca9db92509b910aaf22237f9f1e1..0bc6fc582215306ac5581c86c89f2fb160c37b8c 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -262,6 +262,7 @@ struct rt_read_seg {
        unsigned long rt_delay_ms;
        unsigned long rt_delay_us;
        bool rt_preempted;
+       int rt_cpu;
 };
 static int err_segs_recorded;
 static struct rt_read_seg err_segs[RCUTORTURE_RDR_MAX_SEGS];
@@ -1862,6 +1863,8 @@ static void rcutorture_one_extend(int *readstate, int newstate,
        WARN_ON_ONCE(idxold2 < 0);
        WARN_ON_ONCE(idxold2 & ~RCUTORTURE_RDR_ALLBITS);
        rtrsp->rt_readstate = newstate;
+       if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_CPU))
+               rtrsp->rt_cpu = raw_smp_processor_id();
 
        /* First, put new protection in place to avoid critical-section gap. */
        if (statesnew & RCUTORTURE_RDR_BH)
@@ -3559,8 +3562,10 @@ rcu_torture_cleanup(void)
                                        err_segs[i].rt_delay_us);
                                firsttime = 0;
                        }
-                       pr_cont("%s\n",
-                               err_segs[i].rt_preempted ? "preempted" : "");
+                       pr_cont("%s", err_segs[i].rt_preempted ? "preempted" : "");
+                       if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_LOG_CPU))
+                               pr_cont(" CPU %d", err_segs[i].rt_cpu);
+                       pr_cont("\n");
 
                }
        }