linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 18/20] torture: Make stutter less vulnerable to compilers and races
Date: Fri,  1 Dec 2017 12:09:03 -0800	[thread overview]
Message-ID: <1512158945-27269-18-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20171201200819.GA25519@linux.vnet.ibm.com>

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>
---
 kernel/torture.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/kernel/torture.c b/kernel/torture.c
index 52781e838541..3bcbd4fbfe18 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -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");
-- 
2.5.2

  parent reply	other threads:[~2017-12-01 20:12 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-01 20:08 [PATCH tip/core/rcu 0/20] Torture-test updates for v4.16 Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 01/20] torture: Suppress CPU stall warnings during shutdown ftrace dump Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 02/20] torture: Prepare scripting for shift from %p to %pK Paul E. McKenney
2017-12-04 12:32   ` David Laight
2017-12-04 13:42     ` Paul E. McKenney
2017-12-04 14:13       ` David Laight
2017-12-04 16:11         ` Paul E. McKenney
2017-12-10 12:52           ` Andy Shevchenko
2017-12-10 18:51             ` Paul E. McKenney
2017-12-10 20:39             ` Linus Torvalds
2017-12-10 21:47               ` Paul E. McKenney
2017-12-11 19:59                 ` Kees Cook
2017-12-12 16:08                   ` Paul E. McKenney
     [not found]               ` <87wp1sa55h.fsf@concordia.ellerman.id.au>
     [not found]                 ` <CA+55aFxHdAX_ztDMUyXihhUv_eftntHecGUUaV3qAtGj_ZbKCg@mail.gmail.com>
2017-12-13 12:59                   ` Long live %pK (was Re: [PATCH tip/core/rcu 02/20] torture: Prepare scripting for shift from %p to %pK) Michael Ellerman
2017-12-13 18:21                     ` Linus Torvalds
2017-12-01 20:08 ` [PATCH tip/core/rcu 03/20] rcutorture: Change printk() %p to %pK Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 04/20] torture: Reduce #ifdefs for preempt_schedule() Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 05/20] rcutorture: Preempt RCU-preempt readers more vigorously Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 06/20] rcutorture/configinit: Fix build directory error message Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 07/20] rcutorture: Remove unused script, config2frag.sh Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 08/20] rcutorture/kvm.sh: Remove unused variable, `alldone` Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 09/20] rcutorture/kvm.sh: Use consistent help text for --qemu-args Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 10/20] rcutorture/kvm.sh: Support execution from any directory Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 11/20] rcutorture/kvm-recheck-*: Improve result directory readability check Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 12/20] rcutorture: Simplify logging Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 13/20] rcutorture: Simplify functions.sh include path Paul E. McKenney
2017-12-01 20:08 ` [PATCH tip/core/rcu 14/20] rcutorture/kvm-build.sh: Skip build directory check Paul E. McKenney
2017-12-01 20:09 ` [PATCH tip/core/rcu 15/20] torture: Place all torture-test modules in one MAINTAINERS group Paul E. McKenney
2017-12-01 20:09 ` [PATCH tip/core/rcu 16/20] locking/locktorture: Fix rwsem reader_delay Paul E. McKenney
2017-12-01 20:09 ` [PATCH tip/core/rcu 17/20] locking/locktorture: Fix num reader/writer corner cases Paul E. McKenney
2017-12-01 20:09 ` Paul E. McKenney [this message]
2017-12-01 20:09 ` [PATCH tip/core/rcu 19/20] torture: Eliminate torture_runnable and perf_runnable Paul E. McKenney
2017-12-01 20:09 ` [PATCH tip/core/rcu 20/20] torture: Save a line in stutter_wait(): while -> for Paul E. McKenney

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1512158945-27269-18-git-send-email-paulmck@linux.vnet.ibm.com \
    --to=paulmck@linux.vnet.ibm.com \
    --cc=akpm@linux-foundation.org \
    --cc=dhowells@redhat.com \
    --cc=dipankar@in.ibm.com \
    --cc=edumazet@google.com \
    --cc=fweisbec@gmail.com \
    --cc=jiangshanlai@gmail.com \
    --cc=josh@joshtriplett.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mathieu.desnoyers@efficios.com \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=tglx@linutronix.de \
    --subject='Re: [PATCH tip/core/rcu 18/20] torture: Make stutter less vulnerable to compilers and races' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).