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rcutorture: Also use GP sequence to judge forward progress

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Currently, rcutorture relies solely on the progress of
rcu_torture_writer() to judge grace-period forward progress.  In theory,
this is the gold standard of forward progress, but in practice rcutorture
separately detects and reports rcu_torture_writer() stalls.  This commit
therefore adds the grace-period sequence number (when provided) to the
judgment of grace-period forward progress, which makes it easier to
distinguish between failure of actual grace periods to progress on the
one hand and downstream forward-progress failures on the other.

For example, given this change, if rcu_torture_writer() stalls,
but rcu_torture_fwd_prog() does not complain, then the grace-period
computation is working, which is a hint that the failure lies in callback
processing, wakeup of the rcu_torture_writer() kthread, or similar.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-07-18 15:39:37 -07:00
parent 1b27291b1e
commit 119248bec9
1 changed files with 7 additions and 4 deletions
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11
kernel/rcu/rcutorture.c
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@ -1673,7 +1673,8 @@ static int __init rcu_torture_stall_init(void)
/* Carry out grace-period forward-progress testing. */
static int rcu_torture_fwd_prog(void *args)
{
unsigned long cvar;
unsigned long cver;
unsigned long gps;
int idx;
unsigned long stopat;
bool tested = false;
@ -1681,7 +1682,8 @@ static int rcu_torture_fwd_prog(void *args)
VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");
do {
schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
cvar = READ_ONCE(rcu_torture_current_version);
cver = READ_ONCE(rcu_torture_current_version);
gps = cur_ops->get_gp_seq();
stopat = jiffies + cur_ops->stall_dur() / fwd_progress_div;
while (time_before(jiffies, stopat) && !torture_must_stop()) {
idx = cur_ops->readlock();
@ -1692,8 +1694,9 @@ static int rcu_torture_fwd_prog(void *args)
}
if (!time_before(jiffies, stopat) && !torture_must_stop()) {
tested = true;
WARN_ON_ONCE(cvar ==
READ_ONCE(rcu_torture_current_version));
cver = cver == READ_ONCE(rcu_torture_current_version);
gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps);
WARN_ON_ONCE(cver && gps < 2);
}
/* Avoid slow periods, better to test when busy. */
stutter_wait("rcu_torture_fwd_prog");