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torture: Make stutter less vulnerable to compilers and races 

The stutter_wait() function repeatedly fetched stutter_pause_test, and
should really just fetch it once on each pass.  The races should be
harmless, but why have the races?  Also, the whole point of the value
"2" for stutter_pause_test is to get everyone to start at very nearly
the same time, but the value "2" was the first jiffy of the stutter
rather than the last jiffy of the stutter.

This commit rearranges the code to be more sensible.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-11-21 15:01:02 -08:00
parent 2ce77d16db
commit 4ced3314fd
1 changed files with 17 additions and 16 deletions
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33
kernel/torture.c
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@ -573,18 +573,21 @@ static int stutter;
*/
void stutter_wait(const char *title)
{
int spt;
cond_resched_rcu_qs();
while (READ_ONCE(stutter_pause_test) ||
(torture_runnable && !READ_ONCE(*torture_runnable))) {
if (stutter_pause_test)
if (READ_ONCE(stutter_pause_test) == 1)
schedule_timeout_interruptible(1);
else
while (READ_ONCE(stutter_pause_test))
cond_resched();
else
spt = READ_ONCE(stutter_pause_test);
while (spt || (torture_runnable && !READ_ONCE(*torture_runnable))) {
if (spt == 1) {
schedule_timeout_interruptible(1);
} else if (spt == 2) {
while (READ_ONCE(stutter_pause_test))
cond_resched();
} else {
schedule_timeout_interruptible(round_jiffies_relative(HZ));
}
torture_shutdown_absorb(title);
spt = READ_ONCE(stutter_pause_test);
}
}
EXPORT_SYMBOL_GPL(stutter_wait);
@ -597,17 +600,15 @@ static int torture_stutter(void *arg)
{
VERBOSE_TOROUT_STRING("torture_stutter task started");
do {
if (!torture_must_stop()) {
if (stutter > 1) {
schedule_timeout_interruptible(stutter - 1);
WRITE_ONCE(stutter_pause_test, 2);
}
schedule_timeout_interruptible(1);
if (!torture_must_stop() && stutter > 1) {
WRITE_ONCE(stutter_pause_test, 1);
schedule_timeout_interruptible(stutter - 1);
WRITE_ONCE(stutter_pause_test, 2);
schedule_timeout_interruptible(1);
}
WRITE_ONCE(stutter_pause_test, 0);
if (!torture_must_stop())
schedule_timeout_interruptible(stutter);
WRITE_ONCE(stutter_pause_test, 0);
torture_shutdown_absorb("torture_stutter");
} while (!torture_must_stop());
torture_kthread_stopping("torture_stutter");