[PATCH v2 1/1] rcu/rcuscale: Stop kfree_scale_thread thread(s) after unloading rcuscale

[Qiuxu Zhuo]

When running the 'kfree_rcu_test' test case with commands [1] the call
trace [2] was thrown. This was because the kfree_scale_thread thread(s)
still run after unloading rcuscale and torture modules. Fix the call
trace by invoking kfree_scale_cleanup() from rcu_scale_cleanup() when
removing the rcuscale module.

Additionally, current rcuscale.c defines kfree_scale_cleanup() after
rcu_scale_cleanup(), to avoid the declaration of kfree_scale_cleanup()
when rcu_scale_cleanup() invoking kfree_scale_cleanup(), move
rcu_scale_cleanup() after kfree_scale_cleanup().

[1] modprobe rcuscale kfree_rcu_test=1
    // After some time
    rmmod rcuscale
    rmmod torture

[2] BUG: unable to handle page fault for address: ffffffffc0601a87
    #PF: supervisor instruction fetch in kernel mode
    #PF: error_code(0x0010) - not-present page
    PGD 11de4f067 P4D 11de4f067 PUD 11de51067 PMD 112f4d067 PTE 0
    Oops: 0010 [#1] PREEMPT SMP NOPTI
    CPU: 1 PID: 1798 Comm: kfree_scale_thr Not tainted 6.3.0-rc1-rcu+ #1
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
    RIP: 0010:0xffffffffc0601a87
    Code: Unable to access opcode bytes at 0xffffffffc0601a5d.
    RSP: 0018:ffffb25bc2e57e18 EFLAGS: 00010297
    RAX: 0000000000000000 RBX: ffffffffc061f0b6 RCX: 0000000000000000
    RDX: 0000000000000000 RSI: ffffffff962fd0de RDI: ffffffff962fd0de
    RBP: ffffb25bc2e57ea8 R08: 0000000000000000 R09: 0000000000000000
    R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
    R13: 0000000000000000 R14: 000000000000000a R15: 00000000001c1dbe
    FS:  0000000000000000(0000) GS:ffff921fa2200000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: ffffffffc0601a5d CR3: 000000011de4c006 CR4: 0000000000370ee0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     <TASK>
     ? kvfree_call_rcu+0xf0/0x3a0
     ? kthread+0xf3/0x120
     ? kthread_complete_and_exit+0x20/0x20
     ? ret_from_fork+0x1f/0x30
     </TASK>
    Modules linked in: rfkill sunrpc ... [last unloaded: torture]
    CR2: ffffffffc0601a87
    ---[ end trace 0000000000000000 ]---

Fixes: e6e78b004fa7 ("rcuperf: Add kfree_rcu() performance Tests")
Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
---
v1 -> v2:

 - Move rcu_scale_cleanup() after kfree_scale_cleanup() to eliminate the
   declaration of kfree_scale_cleanup().

 - Remove the unnecessary step "modprobe torture" from the commit message.

 - Add the description for why move rcu_scale_cleanup() after
   kfree_scale_cleanup() to the commit message.

Thanks Paul's comments on eliminating the extra function declaration and
removing the unnecessary "modprobe torture" from the commit message. 

Thanks Joel's constructive comments that for long-term maintenance we may
need to split out the common code within current {ref,rcu}scale.c files.

 kernel/rcu/rcuscale.c | 201 ++++++++++++++++++++++--------------------
 1 file changed, 103 insertions(+), 98 deletions(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 91fb5905a008..5a000d26f03e 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -522,89 +522,6 @@ rcu_scale_print_module_parms(struct rcu_scale_ops *cur_ops, const char *tag)
 		 scale_type, tag, nrealreaders, nrealwriters, verbose, shutdown);
 }
 
-static void
-rcu_scale_cleanup(void)
-{
-	int i;
-	int j;
-	int ngps = 0;
-	u64 *wdp;
-	u64 *wdpp;
-
-	/*
-	 * Would like warning at start, but everything is expedited
-	 * during the mid-boot phase, so have to wait till the end.
-	 */
-	if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp)
-		SCALEOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!");
-	if (rcu_gp_is_normal() && gp_exp)
-		SCALEOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!");
-	if (gp_exp && gp_async)
-		SCALEOUT_ERRSTRING("No expedited async GPs, so went with async!");
-
-	if (torture_cleanup_begin())
-		return;
-	if (!cur_ops) {
-		torture_cleanup_end();
-		return;
-	}
-
-	if (reader_tasks) {
-		for (i = 0; i < nrealreaders; i++)
-			torture_stop_kthread(rcu_scale_reader,
-					     reader_tasks[i]);
-		kfree(reader_tasks);
-	}
-
-	if (writer_tasks) {
-		for (i = 0; i < nrealwriters; i++) {
-			torture_stop_kthread(rcu_scale_writer,
-					     writer_tasks[i]);
-			if (!writer_n_durations)
-				continue;
-			j = writer_n_durations[i];
-			pr_alert("%s%s writer %d gps: %d\n",
-				 scale_type, SCALE_FLAG, i, j);
-			ngps += j;
-		}
-		pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n",
-			 scale_type, SCALE_FLAG,
-			 t_rcu_scale_writer_started, t_rcu_scale_writer_finished,
-			 t_rcu_scale_writer_finished -
-			 t_rcu_scale_writer_started,
-			 ngps,
-			 rcuscale_seq_diff(b_rcu_gp_test_finished,
-					   b_rcu_gp_test_started));
-		for (i = 0; i < nrealwriters; i++) {
-			if (!writer_durations)
-				break;
-			if (!writer_n_durations)
-				continue;
-			wdpp = writer_durations[i];
-			if (!wdpp)
-				continue;
-			for (j = 0; j < writer_n_durations[i]; j++) {
-				wdp = &wdpp[j];
-				pr_alert("%s%s %4d writer-duration: %5d %llu\n",
-					scale_type, SCALE_FLAG,
-					i, j, *wdp);
-				if (j % 100 == 0)
-					schedule_timeout_uninterruptible(1);
-			}
-			kfree(writer_durations[i]);
-		}
-		kfree(writer_tasks);
-		kfree(writer_durations);
-		kfree(writer_n_durations);
-	}
-
-	/* Do torture-type-specific cleanup operations.  */
-	if (cur_ops->cleanup != NULL)
-		cur_ops->cleanup();
-
-	torture_cleanup_end();
-}
-
 /*
  * Return the number if non-negative.  If -1, the number of CPUs.
  * If less than -1, that much less than the number of CPUs, but
@@ -624,21 +541,6 @@ static int compute_real(int n)
 	return nr;
 }
 
-/*
- * RCU scalability shutdown kthread.  Just waits to be awakened, then shuts
- * down system.
- */
-static int
-rcu_scale_shutdown(void *arg)
-{
-	wait_event(shutdown_wq,
-		   atomic_read(&n_rcu_scale_writer_finished) >= nrealwriters);
-	smp_mb(); /* Wake before output. */
-	rcu_scale_cleanup();
-	kernel_power_off();
-	return -EINVAL;
-}
-
 /*
  * kfree_rcu() scalability tests: Start a kfree_rcu() loop on all CPUs for number
  * of iterations and measure total time and number of GP for all iterations to complete.
@@ -875,6 +777,109 @@ kfree_scale_init(void)
 	return firsterr;
 }
 
+static void
+rcu_scale_cleanup(void)
+{
+	int i;
+	int j;
+	int ngps = 0;
+	u64 *wdp;
+	u64 *wdpp;
+
+	/*
+	 * Would like warning at start, but everything is expedited
+	 * during the mid-boot phase, so have to wait till the end.
+	 */
+	if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp)
+		SCALEOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!");
+	if (rcu_gp_is_normal() && gp_exp)
+		SCALEOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!");
+	if (gp_exp && gp_async)
+		SCALEOUT_ERRSTRING("No expedited async GPs, so went with async!");
+
+	if (kfree_rcu_test) {
+		kfree_scale_cleanup();
+		return;
+	}
+
+	if (torture_cleanup_begin())
+		return;
+	if (!cur_ops) {
+		torture_cleanup_end();
+		return;
+	}
+
+	if (reader_tasks) {
+		for (i = 0; i < nrealreaders; i++)
+			torture_stop_kthread(rcu_scale_reader,
+					     reader_tasks[i]);
+		kfree(reader_tasks);
+	}
+
+	if (writer_tasks) {
+		for (i = 0; i < nrealwriters; i++) {
+			torture_stop_kthread(rcu_scale_writer,
+					     writer_tasks[i]);
+			if (!writer_n_durations)
+				continue;
+			j = writer_n_durations[i];
+			pr_alert("%s%s writer %d gps: %d\n",
+				 scale_type, SCALE_FLAG, i, j);
+			ngps += j;
+		}
+		pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n",
+			 scale_type, SCALE_FLAG,
+			 t_rcu_scale_writer_started, t_rcu_scale_writer_finished,
+			 t_rcu_scale_writer_finished -
+			 t_rcu_scale_writer_started,
+			 ngps,
+			 rcuscale_seq_diff(b_rcu_gp_test_finished,
+					   b_rcu_gp_test_started));
+		for (i = 0; i < nrealwriters; i++) {
+			if (!writer_durations)
+				break;
+			if (!writer_n_durations)
+				continue;
+			wdpp = writer_durations[i];
+			if (!wdpp)
+				continue;
+			for (j = 0; j < writer_n_durations[i]; j++) {
+				wdp = &wdpp[j];
+				pr_alert("%s%s %4d writer-duration: %5d %llu\n",
+					scale_type, SCALE_FLAG,
+					i, j, *wdp);
+				if (j % 100 == 0)
+					schedule_timeout_uninterruptible(1);
+			}
+			kfree(writer_durations[i]);
+		}
+		kfree(writer_tasks);
+		kfree(writer_durations);
+		kfree(writer_n_durations);
+	}
+
+	/* Do torture-type-specific cleanup operations.  */
+	if (cur_ops->cleanup != NULL)
+		cur_ops->cleanup();
+
+	torture_cleanup_end();
+}
+
+/*
+ * RCU scalability shutdown kthread.  Just waits to be awakened, then shuts
+ * down system.
+ */
+static int
+rcu_scale_shutdown(void *arg)
+{
+	wait_event(shutdown_wq,
+		   atomic_read(&n_rcu_scale_writer_finished) >= nrealwriters);
+	smp_mb(); /* Wake before output. */
+	rcu_scale_cleanup();
+	kernel_power_off();
+	return -EINVAL;
+}
+
 static int __init
 rcu_scale_init(void)
 {
-- 
2.17.1