Commit 579a05da authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Uladzislau Rezki (Sony)
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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: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
parent 5ec09001

kernel/rcu/Kconfig.debug

+15 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcu/rcutorture.c

+7 −2
Original line number Diff line number Diff line
@@ -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");



		}

	}