[PATCH rcu 0/6] Torture-test updates for v5.19

[PATCH rcu 0/6] Torture-test updates for v5.19

[Paul E. McKenney]

Hello!

This series contains torture-test updates fixing some bugs in tests and
closing some testing holes.

1.	Add rcu_normal and rcu_expedited runs to torture.sh.

2.	Suppress debugging grace period delays during flooding.

3.	Fix distribution of short handler delays.

4.	Avoid corner-case #DE with nsynctypes check, courtesy of David
	Vernet.

5.	Add missing return and use __func__ in warning, courtesy of
	David Vernet.

6.	Call preempt_schedule() through static call/key, courtesy of
	Frederic Weisbecker.

						Thanx, Paul

------------------------------------------------------------------------

 b/include/linux/torture.h                           |    2 -
 b/kernel/rcu/rcu.h                                  |    4 ++
 b/kernel/rcu/rcutorture.c                           |    4 ++
 b/kernel/rcu/tree.c                                 |   32 ++++++++++++++++++--
 b/kernel/scftorture.c                               |    5 +--
 b/tools/testing/selftests/rcutorture/bin/torture.sh |   18 +++++++++++
 kernel/rcu/rcutorture.c                             |   14 ++++++++
 7 files changed, 72 insertions(+), 7 deletions(-)

[PATCH rcu 1/6] torture: Add rcu_normal and rcu_expedited runs to torture.sh

[Paul E. McKenney]

Currently, the rcupdate.rcu_normal and rcupdate.rcu_expedited kernel
boot parameters are not regularly tested.  The potential addition of
polled expedited grace-period APIs increases the amount of code that is
affected by these kernel boot parameters.  This commit therefore adds a
"--do-rt" argument to torture.sh to exercise these kernel-boot options.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 .../selftests/rcutorture/bin/torture.sh        | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tools/testing/selftests/rcutorture/bin/torture.sh b/tools/testing/selftests/rcutorture/bin/torture.sh
index bfe09e2829c8..e657a6e06417 100755
--- a/tools/testing/selftests/rcutorture/bin/torture.sh
+++ b/tools/testing/selftests/rcutorture/bin/torture.sh
@@ -54,6 +54,7 @@ do_kvfree=yes
 do_kasan=yes
 do_kcsan=no
 do_clocksourcewd=yes
+do_rt=yes
 
 # doyesno - Helper function for yes/no arguments
 function doyesno () {
@@ -82,6 +83,7 @@ usage () {
 	echo "       --do-rcuscale / --do-no-rcuscale"
 	echo "       --do-rcutorture / --do-no-rcutorture"
 	echo "       --do-refscale / --do-no-refscale"
+	echo "       --do-rt / --do-no-rt"
 	echo "       --do-scftorture / --do-no-scftorture"
 	echo "       --duration [ <minutes> | <hours>h | <days>d ]"
 	echo "       --kcsan-kmake-arg kernel-make-arguments"
@@ -118,6 +120,7 @@ do
 		do_scftorture=yes
 		do_rcuscale=yes
 		do_refscale=yes
+		do_rt=yes
 		do_kvfree=yes
 		do_kasan=yes
 		do_kcsan=yes
@@ -148,6 +151,7 @@ do
 		do_scftorture=no
 		do_rcuscale=no
 		do_refscale=no
+		do_rt=no
 		do_kvfree=no
 		do_kasan=no
 		do_kcsan=no
@@ -162,6 +166,9 @@ do
 	--do-refscale|--do-no-refscale)
 		do_refscale=`doyesno "$1" --do-refscale`
 		;;
+	--do-rt|--do-no-rt)
+		do_rt=`doyesno "$1" --do-rt`
+		;;
 	--do-scftorture|--do-no-scftorture)
 		do_scftorture=`doyesno "$1" --do-scftorture`
 		;;
@@ -354,6 +361,17 @@ then
 	torture_set "scftorture" tools/testing/selftests/rcutorture/bin/kvm.sh --torture scf --allcpus --duration "$duration_scftorture" --configs "$configs_scftorture" --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --memory 1G --trust-make
 fi
 
+if test "$do_rt" = "yes"
+then
+	# With all post-boot grace periods forced to normal.
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_normal=1"
+	torture_set "rcurttorture" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --trust-make
+
+	# With all post-boot grace periods forced to expedited.
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_expedited=1"
+	torture_set "rcurttorture-exp" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --trust-make
+fi
+
 if test "$do_refscale" = yes
 then
 	primlist="`grep '\.name[ 	]*=' kernel/rcu/refscale.c | sed -e 's/^[^"]*"//' -e 's/".*$//'`"
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 2/6] rcutorture: Suppress debugging grace period delays during flooding

[Paul E. McKenney]

Tree RCU supports grace-period delays using the rcutree.gp_cleanup_delay,
rcutree.gp_init_delay, and rcutree.gp_preinit_delay kernel boot
parameters.  These delays are strictly for debugging purposes, and have
proven quite effective at exposing bugs involving race with CPU-hotplug
operations.  However, these delays can result in false positives when
used in conjunction with callback flooding, for example, those generated
by the rcutorture.fwd_progress kernel boot parameter.

This commit therefore suppresses grace-period delays while callback
flooding is in progress.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/rcu.h        |  4 ++++
 kernel/rcu/rcutorture.c |  4 ++++
 kernel/rcu/tree.c       | 32 +++++++++++++++++++++++++++++---
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 24b5f2c2de87..7a221393fcdb 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -523,6 +523,8 @@ static inline bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) { ret
 static inline void show_rcu_gp_kthreads(void) { }
 static inline int rcu_get_gp_kthreads_prio(void) { return 0; }
 static inline void rcu_fwd_progress_check(unsigned long j) { }
+static inline void rcu_gp_slow_register(atomic_t *rgssp) { }
+static inline void rcu_gp_slow_unregister(atomic_t *rgssp) { }
 #else /* #ifdef CONFIG_TINY_RCU */
 bool rcu_dynticks_zero_in_eqs(int cpu, int *vp);
 unsigned long rcu_get_gp_seq(void);
@@ -535,6 +537,8 @@ void rcu_fwd_progress_check(unsigned long j);
 void rcu_force_quiescent_state(void);
 extern struct workqueue_struct *rcu_gp_wq;
 extern struct workqueue_struct *rcu_par_gp_wq;
+void rcu_gp_slow_register(atomic_t *rgssp);
+void rcu_gp_slow_unregister(atomic_t *rgssp);
 #endif /* #else #ifdef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_RCU_NOCB_CPU
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 55d049c39608..f37b7a01dcd0 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2916,10 +2916,12 @@ rcu_torture_cleanup(void)
 			pr_info("%s: Invoking %pS().\n", __func__, cur_ops->cb_barrier);
 			cur_ops->cb_barrier();
 		}
+		rcu_gp_slow_unregister(NULL);
 		return;
 	}
 	if (!cur_ops) {
 		torture_cleanup_end();
+		rcu_gp_slow_unregister(NULL);
 		return;
 	}
 
@@ -3016,6 +3018,7 @@ rcu_torture_cleanup(void)
 	else
 		rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
 	torture_cleanup_end();
+	rcu_gp_slow_unregister(&rcu_fwd_cb_nodelay);
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
@@ -3320,6 +3323,7 @@ rcu_torture_init(void)
 	if (object_debug)
 		rcu_test_debug_objects();
 	torture_init_end();
+	rcu_gp_slow_register(&rcu_fwd_cb_nodelay);
 	return 0;
 
 unwind:
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a4b8189455d5..db67dae8ed88 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1705,11 +1705,37 @@ static void note_gp_changes(struct rcu_data *rdp)
 		rcu_gp_kthread_wake();
 }
 
+static atomic_t *rcu_gp_slow_suppress;
+
+/* Register a counter to suppress debugging grace-period delays. */
+void rcu_gp_slow_register(atomic_t *rgssp)
+{
+	WARN_ON_ONCE(rcu_gp_slow_suppress);
+
+	WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
+
+/* Unregister a counter, with NULL for not caring which. */
+void rcu_gp_slow_unregister(atomic_t *rgssp)
+{
+	WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
+
+	WRITE_ONCE(rcu_gp_slow_suppress, NULL);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
+
+static bool rcu_gp_slow_is_suppressed(void)
+{
+	atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
+
+	return rgssp && atomic_read(rgssp);
+}
+
 static void rcu_gp_slow(int delay)
 {
-	if (delay > 0 &&
-	    !(rcu_seq_ctr(rcu_state.gp_seq) %
-	      (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
+	if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
+	    !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
 		schedule_timeout_idle(delay);
 }
 
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 3/6] scftorture: Fix distribution of short handler delays

[Paul E. McKenney]

The scftorture test module's scf_handler() function is supposed to provide
three different distributions of short delays (including "no delay") and
one distribution of long delays, if specified by the scftorture.longwait
module parameter.  However, the second of the two non-zero-wait short delays
is disabled due to the first such delay's "goto out" not being enclosed in
the "then" clause with the "udelay()".

This commit therefore adjusts the code to provide the intended set of
delays.

Fixes: e9d338a0b179 ("scftorture: Add smp_call_function() torture test")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/scftorture.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/scftorture.c b/kernel/scftorture.c
index dcb0410950e4..5d113aa59e77 100644
--- a/kernel/scftorture.c
+++ b/kernel/scftorture.c
@@ -267,9 +267,10 @@ static void scf_handler(void *scfc_in)
 	}
 	this_cpu_inc(scf_invoked_count);
 	if (longwait <= 0) {
-		if (!(r & 0xffc0))
+		if (!(r & 0xffc0)) {
 			udelay(r & 0x3f);
-		goto out;
+			goto out;
+		}
 	}
 	if (r & 0xfff)
 		goto out;
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 4/6] rcutorture: Avoid corner-case #DE with nsynctypes check

[Paul E. McKenney]

From: David Vernet <void@manifault.com>

The rcutorture module is used to run torture tests that validate RCU.
rcutorture takes a variety of module parameters that configure the
functionality of the test. Amongst these parameters are the types of
synchronization mechanisms that the rcu_torture_writer and
rcu_torture_fakewriter tasks may use, and the torture_type of the run which
determines what read and sync operations are used by the various writer and
reader tasks that run throughout the test.

When the module is configured to only use sync types for which the
specified torture_type does not implement the necessary operations, we can
end up in a state where nsynctypes is 0. This is not an erroneous state,
but it currently crashes the kernel with a #DE due to nsynctypes being used
with a modulo operator in rcu_torture_fakewriter().

Here is an example of such a #DE:

$ insmod ./rcutorture.ko gp_cond=1 gp_cond_exp=0 gp_exp=0 gp_poll_exp=0
gp_normal=0 gp_poll=0 gp_poll_exp=0 verbose=9999 torture_type=trivial

...

[ 8536.525096] divide error: 0000 [#1] PREEMPT SMP PTI
[ 8536.525101] CPU: 30 PID: 392138 Comm: rcu_torture_fak Kdump: loaded Tainted: G S                5.17.0-rc1-00179-gc8c42c80febd #24
[ 8536.525105] Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A23 12/08/2020
[ 8536.525106] RIP: 0010:rcu_torture_fakewriter+0xf1/0x2d0 [rcutorture]
[ 8536.525121] Code: 00 31 d2 8d 0c f5 00 00 00 00 48 63 c9 48 f7 f1 48 85 d2 0f 84 79 ff ff ff 48 89 e7 e8 78 78 01 00 48 63 0d 29 ca 00 00 31 d2 <48> f7 f1 8b 04 95 00 05 4e a0 83 f8 06 0f 84 ad 00 00 00 7f 1f 83
[ 8536.525124] RSP: 0018:ffffc9000777fef0 EFLAGS: 00010246
[ 8536.525127] RAX: 00000000223d006e RBX: cccccccccccccccd RCX: 0000000000000000
[ 8536.525130] RDX: 0000000000000000 RSI: ffffffff824315b9 RDI: ffffc9000777fef0
[ 8536.525132] RBP: ffffc9000487bb30 R08: 0000000000000002 R09: 000000000002a580
[ 8536.525134] R10: ffffffff82c5f920 R11: 0000000000000000 R12: ffff8881a2c35d00
[ 8536.525136] R13: ffff8881540c8d00 R14: ffffffffa04d39d0 R15: 0000000000000000
[ 8536.525137] FS:  0000000000000000(0000) GS:ffff88903ff80000(0000) knlGS:0000000000000000
[ 8536.525140] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 8536.525142] CR2: 00007f839f022000 CR3: 0000000002c0a006 CR4: 00000000007706e0
[ 8536.525144] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 8536.525145] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 8536.525147] PKRU: 55555554
[ 8536.525148] Call Trace:
[ 8536.525150]  <TASK>
[ 8536.525153]  kthread+0xe8/0x110
[ 8536.525161]  ? kthread_complete_and_exit+0x20/0x20
[ 8536.525167]  ret_from_fork+0x22/0x30
[ 8536.525174]  </TASK>

The solution is to gracefully handle the case of nsynctypes being 0 in
rcu_torture_fakewriter() by not performing any work. This is already being
done in rcu_torture_writer(), though there is a missing return on that path
which will be fixed in a subsequent patch.

Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/rcutorture.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f37b7a01dcd0..d5105fb6c980 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1322,6 +1322,17 @@ rcu_torture_fakewriter(void *arg)
 	VERBOSE_TOROUT_STRING("rcu_torture_fakewriter task started");
 	set_user_nice(current, MAX_NICE);
 
+	if (WARN_ONCE(nsynctypes == 0,
+		      "%s: No update-side primitives.\n", __func__)) {
+		/*
+		 * No updates primitives, so don't try updating.
+		 * The resulting test won't be testing much, hence the
+		 * above WARN_ONCE().
+		 */
+		torture_kthread_stopping("rcu_torture_fakewriter");
+		return 0;
+	}
+
 	do {
 		torture_hrtimeout_jiffies(torture_random(&rand) % 10, &rand);
 		if (cur_ops->cb_barrier != NULL &&
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 5/6] rcutorture: Add missing return and use __func__ in warning

[Paul E. McKenney]

From: David Vernet <void@manifault.com>

The rcutorture module has an rcu_torture_writer task that repeatedly
performs writes, synchronizations, and deletes. There is a corner-case
check in rcu_torture_writer() wherein if nsynctypes is 0, a warning is
issued and the task waits to be stopped via a call to
torture_kthread_stopping() rather than performing any work.

There should be a return statement following this call to
torture_kthread_stopping(), as the intention with issuing the call to
torture_kthread_stopping() in the first place is to avoid the
rcu_torture_writer task from performing any work. Some of the work may even
be dangerous to perform, such as potentially causing a #DE due to
nsynctypes being used in a modulo operator when querying for sync updates
to issue.

This patch adds the missing return call.  As a bonus, it also fixes a
checkpatch warning that was emitted due to the WARN_ONCE() call using the
name of the function rather than __func__.

Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/rcutorture.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d5105fb6c980..f1292d9e86b5 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1178,7 +1178,7 @@ rcu_torture_writer(void *arg)
 			 " GP expediting controlled from boot/sysfs for %s.\n",
 			 torture_type, cur_ops->name);
 	if (WARN_ONCE(nsynctypes == 0,
-		      "rcu_torture_writer: No update-side primitives.\n")) {
+		      "%s: No update-side primitives.\n", __func__)) {
 		/*
 		 * No updates primitives, so don't try updating.
 		 * The resulting test won't be testing much, hence the
@@ -1186,6 +1186,7 @@ rcu_torture_writer(void *arg)
 		 */
 		rcu_torture_writer_state = RTWS_STOPPING;
 		torture_kthread_stopping("rcu_torture_writer");
+		return 0;
 	}
 
 	do {
-- 
2.31.1.189.g2e36527f23

[PATCH rcu 6/6] rcutorture: Call preempt_schedule() through static call/key

[Paul E. McKenney]

From: Frederic Weisbecker <frederic@kernel.org>

The rcutorture test suite sometimess triggers a random scheduler
preemption call while simulating a read delay.  Unfortunately, its
direct call to preempt_schedule() bypasses the static call/key filter
used by CONFIG_PREEMPT_DYNAMIC.  This breaks the no-preempt assumption
when the dynamic preemption mode is "none".

For example, rcu_blocking_is_gp() is fooled and abbreviates grace periods
when the CPU runs in no-preempt UP mode.

Fix this by making torture_preempt_schedule() call __preempt_schedule(),
which uses the static call/key.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/torture.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/torture.h b/include/linux/torture.h
index 63fa4196e51c..7038104463e4 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -118,7 +118,7 @@ void _torture_stop_kthread(char *m, struct task_struct **tp);
 	_torture_stop_kthread("Stopping " #n " task", &(tp))
 
 #ifdef CONFIG_PREEMPTION
-#define torture_preempt_schedule() preempt_schedule()
+#define torture_preempt_schedule() __preempt_schedule()
 #else
 #define torture_preempt_schedule()	do { } while (0)
 #endif
-- 
2.31.1.189.g2e36527f23