Commit 1afb95fe authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

torture: Maintain torture-specific set of CPUs-online books 



The TREE01 rcutorture scenario intentionally creates confusion as to the
number of available CPUs by specifying the "maxcpus=8 nr_cpus=43" kernel
boot parameters.  This can disable rcutorture's load shedding, which
currently uses num_online_cpus(), which would count the extra 35 CPUs.
However, the rcutorture guest OS will be provisioned with only 8 CPUs,
which means that rcutorture will present full load even when all but one
of the original 8 CPUs are offline.  This can result in spurious errors
due to extreme overloading of that single remaining CPU.

This commit therefore keeps a separate set of books on the number of
usable online CPUs, so that torture_num_online_cpus() is used for load
shedding instead of num_online_cpus().  Note that initial sizing must
use num_online_cpus() because torture_num_online_cpus() will return
NR_CPUS until shortly after torture_onoff_init() is invoked.

Reported-by: default avatarFrederic Weisbecker <frederic@kernel.org>
[ paulmck: Apply feedback from kernel test robot. ]
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 0b962c8f

include/linux/torture.h

+5 −0
Original line number Diff line number Diff line
@@ -48,6 +48,11 @@ do { \ 
void verbose_torout_sleep(void);



/* Definitions for online/offline exerciser. */

#ifdef CONFIG_HOTPLUG_CPU

int torture_num_online_cpus(void);

#else /* #ifdef CONFIG_HOTPLUG_CPU */

static inline int torture_num_online_cpus(void) { return 1; }

#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */

typedef void torture_ofl_func(void);

bool torture_offline(int cpu, long *n_onl_attempts, long *n_onl_successes,

		     unsigned long *sum_offl, int *min_onl, int *max_onl);

kernel/rcu/rcutorture.c

+2 −2
Original line number Diff line number Diff line
@@ -1338,7 +1338,7 @@ static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp, 
					struct torture_random_state *trsp)

{

	unsigned long loops;

	int noc = num_online_cpus();

	int noc = torture_num_online_cpus();

	int rdrchked;

	int rdrchker;

	struct rcu_torture_reader_check *rtrcp; // Me.
@@ -1658,7 +1658,7 @@ rcu_torture_reader(void *arg) 
			torture_hrtimeout_us(500, 1000, &rand);

			lastsleep = jiffies + 10;

		}

		while (num_online_cpus() < mynumonline && !torture_must_stop())

		while (torture_num_online_cpus() < mynumonline && !torture_must_stop())

			schedule_timeout_interruptible(HZ / 5);

		stutter_wait("rcu_torture_reader");

	} while (!torture_must_stop());

kernel/torture.c

+16 −0
Original line number Diff line number Diff line
@@ -175,6 +175,19 @@ static unsigned long sum_online; 
static int min_online = -1;

static int max_online;



static int torture_online_cpus = NR_CPUS;



/*

 * Some torture testing leverages confusion as to the number of online

 * CPUs.  This function returns the torture-testing view of this number,

 * which allows torture tests to load-balance appropriately.

 */

int torture_num_online_cpus(void)

{

	return READ_ONCE(torture_online_cpus);

}

EXPORT_SYMBOL_GPL(torture_num_online_cpus);



/*

 * Attempt to take a CPU offline.  Return false if the CPU is already

 * offline or if it is not subject to CPU-hotplug operations.  The
@@ -229,6 +242,8 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes, 
			*min_offl = delta;

		if (*max_offl < delta)

			*max_offl = delta;

		WRITE_ONCE(torture_online_cpus, torture_online_cpus - 1);

		WARN_ON_ONCE(torture_online_cpus <= 0);

	}



	return true;
@@ -285,6 +300,7 @@ bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes, 
			*min_onl = delta;

		if (*max_onl < delta)

			*max_onl = delta;

		WRITE_ONCE(torture_online_cpus, torture_online_cpus + 1);

	}



	return true;