[PATCH tip/core/rcu 18/28] rcutorture: Make stutter_wait() caller restore priority

paulmck
2020-11-05T23:48:37Z

Currently, stutter_wait() will happily spin waiting for the stutter
interval to end even if the caller is running at a real-time priority
level. This could starve normal-priority tasks for no good reason. This
commit therefore drops the calling task's priority to SCHED_OTHER MAX_NICE
if stutter_wait() needs to wait. But when it waits, stutter_wait()
returns true, which allows the caller to restore the priority if needed.
Callers that were already running at SCHED_OTHER MAX_NICE obviously
do not need any changes, but this commit also restores priority for
higher-priority callers.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/rcutorture.c | 24 ++++++++++++++++++------
kernel/torture.c | 9 ++++-----
2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index db37671..4391d2f 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -912,7 +912,8 @@ static int rcu_torture_boost(void *arg)
oldstarttime = boost_starttime;
while (time_before(jiffies, oldstarttime)) {
schedule_timeout_interruptible(oldstarttime - jiffies);
- stutter_wait("rcu_torture_boost");
+ if (stutter_wait("rcu_torture_boost"))
+ sched_set_fifo_low(current);
if (torture_must_stop())
goto checkwait;
}
@@ -932,7 +933,8 @@ static int rcu_torture_boost(void *arg)
jiffies);
call_rcu_time = jiffies;
}
- stutter_wait("rcu_torture_boost");
+ if (stutter_wait("rcu_torture_boost"))
+ sched_set_fifo_low(current);
if (torture_must_stop())
goto checkwait;
}
@@ -964,7 +966,8 @@ static int rcu_torture_boost(void *arg)
}

/* Go do the stutter. */
-checkwait: stutter_wait("rcu_torture_boost");
+checkwait: if (stutter_wait("rcu_torture_boost"))
+ sched_set_fifo_low(current);
} while (!torture_must_stop());

/* Clean up and exit. */
@@ -987,6 +990,7 @@ rcu_torture_fqs(void *arg)
{
unsigned long fqs_resume_time;
int fqs_burst_remaining;
+ int oldnice = task_nice(current);

VERBOSE_TOROUT_STRING("rcu_torture_fqs task started");
do {
@@ -1002,7 +1006,8 @@ rcu_torture_fqs(void *arg)
udelay(fqs_holdoff);
fqs_burst_remaining -= fqs_holdoff;
}
- stutter_wait("rcu_torture_fqs");
+ if (stutter_wait("rcu_torture_fqs"))
+ sched_set_normal(current, oldnice);
} while (!torture_must_stop());
torture_kthread_stopping("rcu_torture_fqs");
return 0;
@@ -1022,9 +1027,11 @@ rcu_torture_writer(void *arg)
bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal;
bool gp_sync1 = gp_sync;
int i;
+ int oldnice = task_nice(current);
struct rcu_torture *rp;
struct rcu_torture *old_rp;
static DEFINE_TORTURE_RANDOM(rand);
+ bool stutter_waited;
int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC,
RTWS_COND_GET, RTWS_SYNC };
int nsynctypes = 0;
@@ -1143,7 +1150,8 @@ rcu_torture_writer(void *arg)
!rcu_gp_is_normal();
}
rcu_torture_writer_state = RTWS_STUTTER;
- if (stutter_wait("rcu_torture_writer") &&
+ stutter_waited = stutter_wait("rcu_torture_writer");
+ if (stutter_waited &&
!READ_ONCE(rcu_fwd_cb_nodelay) &&
!cur_ops->slow_gps &&
!torture_must_stop() &&
@@ -1155,6 +1163,8 @@ rcu_torture_writer(void *arg)
rcu_ftrace_dump(DUMP_ALL);
WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);
}
+ if (stutter_waited)
+ sched_set_normal(current, oldnice);
} while (!torture_must_stop());
rcu_torture_current = NULL; // Let stats task know that we are done.
/* Reset expediting back to unexpedited. */
@@ -2103,6 +2113,7 @@ static struct notifier_block rcutorture_oom_nb = {
/* Carry out grace-period forward-progress testing. */
static int rcu_torture_fwd_prog(void *args)
{
+ int oldnice = task_nice(current);
struct rcu_fwd *rfp = args;
int tested = 0;
int tested_tries = 0;
@@ -2121,7 +2132,8 @@ static int rcu_torture_fwd_prog(void *args)
rcu_torture_fwd_prog_cr(rfp);

/* Avoid slow periods, better to test when busy. */
- stutter_wait("rcu_torture_fwd_prog");
+ if (stutter_wait("rcu_torture_fwd_prog"))
+ sched_set_normal(current, oldnice);
} while (!torture_must_stop());
/* Short runs might not contain a valid forward-progress attempt. */
WARN_ON(!tested && tested_tries >= 5);
diff --git a/kernel/torture.c b/kernel/torture.c
index d8bdd9a..8995ed1 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -604,19 +604,19 @@ bool stutter_wait(const char *title)
{
ktime_t delay;
unsigned i = 0;
- int oldnice;
bool ret = false;
int spt;

cond_resched_tasks_rcu_qs();
spt = READ_ONCE(stutter_pause_test);
for (; spt; spt = READ_ONCE(stutter_pause_test)) {
- ret = true;
+ if (!ret) {
+ sched_set_normal(current, MAX_NICE);
+ ret = true;
+ }
if (spt == 1) {
schedule_timeout_interruptible(1);
} else if (spt == 2) {
- oldnice = task_nice(current);
- set_user_nice(current, MAX_NICE);
while (READ_ONCE(stutter_pause_test)) {
if (!(i++ & 0xffff)) {
set_current_state(TASK_INTERRUPTIBLE);
@@ -625,7 +625,6 @@ bool stutter_wait(const char *title)
}
cond_resched();
}
- set_user_nice(current, oldnice);
} else {
schedule_timeout_interruptible(round_jiffies_relative(HZ));
}
--
2.9.5