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rcutorture: Add self-propagating callback to forward-progress testing 

If rcutorture is run on a quiet system with the rcutorture.stutter module
parameter set high, then there can legitimately be an extended period
during which no RCU forward progress takes place.  This can result
in false-positive no-forward-progress splats.  This commit therefore
makes rcu_torture_fwd_prog() create a self-propagating RCU callback
to ensure that grace periods are in progress for the duration of the
forward-progress test.

Note that the RCU flavor under test must define ->call(), ->sync(),
and ->cb_barrier() for this self-propagating callback to be created.
If one or more of those rcu_torture_ops fields are NULL, then the
rcu_torture_fwd_prog() function will silently proceed without creating
the self-propagating callback.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
hifive-unleashed-5.1
Paul E. McKenney 2018-07-19 13:36:00 -07:00
parent 08a7a2ec68
commit 9fdcb9afe0
1 changed files with 36 additions and 0 deletions
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36
kernel/rcu/rcutorture.c
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@ -1670,20 +1670,49 @@ static int __init rcu_torture_stall_init(void)
return torture_create_kthread(rcu_torture_stall, NULL, stall_task);
}
/* State structure for forward-progress self-propagating RCU callback. */
struct fwd_cb_state {
struct rcu_head rh;
int stop;
};
/*
* Forward-progress self-propagating RCU callback function. Because
* callbacks run from softirq, this function is an implicit RCU read-side
* critical section.
*/
static void rcu_torture_fwd_prog_cb(struct rcu_head *rhp)
{
struct fwd_cb_state *fcsp = container_of(rhp, struct fwd_cb_state, rh);
if (READ_ONCE(fcsp->stop)) {
WRITE_ONCE(fcsp->stop, 2);
return;
}
cur_ops->call(&fcsp->rh, rcu_torture_fwd_prog_cb);
}
/* Carry out grace-period forward-progress testing. */
static int rcu_torture_fwd_prog(void *args)
{
unsigned long cver;
struct fwd_cb_state fcs = { .stop = 0 };
unsigned long gps;
int idx;
int sd;
int sd4;
bool selfpropcb = false;
unsigned long stopat;
bool tested = false;
int tested_tries = 0;
static DEFINE_TORTURE_RANDOM(trs);
VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");
if (cur_ops->call && cur_ops->sync && cur_ops->cb_barrier) {
init_rcu_head_on_stack(&fcs.rh);
cur_ops->call(&fcs.rh, rcu_torture_fwd_prog_cb);
selfpropcb = true;
}
do {
schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
cver = READ_ONCE(rcu_torture_current_version);
@ -1708,6 +1737,13 @@ static int rcu_torture_fwd_prog(void *args)
/* Avoid slow periods, better to test when busy. */
stutter_wait("rcu_torture_fwd_prog");
} while (!torture_must_stop());
if (selfpropcb) {
WRITE_ONCE(fcs.stop, 1);
cur_ops->sync(); /* Wait for running callback to complete. */
cur_ops->cb_barrier(); /* Wait for queued callbacks. */
WARN_ON(READ_ONCE(fcs.stop) != 2);
destroy_rcu_head_on_stack(&fcs.rh);
}
/* Short runs might not contain a valid forward-progress attempt. */
WARN_ON(!tested && tested_tries >= 5);
torture_kthread_stopping("rcu_torture_fwd_prog");