From cf7c1af65e94da3efa220e54f01f60a50496b322 Mon Sep 17 00:00:00 2001
From: Li Zhijian <lizhijian@cn.fujitsu.com>
Date: Mon, 25 Oct 2021 11:26:57 +0800
Subject: [PATCH] refscale: Prevent buffer to pr_alert() being too long

References: bnc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.17-rc0
Git-commit: 9880eb878c315b241002d43d7ff89df23713a51b

0Day/LKP observed that the refscale results fail to complete when larger
values of nrun (such as 300) are specified.  The problem is that printk()
can accept at most a 1024-byte buffer.  This commit therefore prints
the buffer whenever its length exceeds 800 bytes.

CC: Philip Li <philip.li@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 kernel/rcu/refscale.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 356f8a9f4e42..cd1877f28968 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -570,7 +570,7 @@ static u64 process_durations(int n)
 	char *buf;
 	u64 sum = 0;
 
-	buf = kmalloc(128 + nreaders * 32, GFP_KERNEL);
+	buf = kmalloc(800 + 64, GFP_KERNEL);
 	if (!buf)
 		return 0;
 	buf[0] = 0;
@@ -583,13 +583,15 @@ static u64 process_durations(int n)
 
 		if (i % 5 == 0)
 			strcat(buf, "\n");
+		if (strlen(buf) >= 800) {
+			pr_alert("%s", buf);
+			buf[0] = 0;
+		}
 		strcat(buf, buf1);
 
 		sum += rt->last_duration_ns;
 	}
-	strcat(buf, "\n");
-
-	SCALEOUT("%s\n", buf);
+	pr_alert("%s\n", buf);
 
 	kfree(buf);
 	return sum;
@@ -613,7 +615,7 @@ static int main_func(void *arg)
 
 	VERBOSE_SCALEOUT("main_func task started");
 	result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL);
-	buf = kzalloc(64 + nruns * 32, GFP_KERNEL);
+	buf = kzalloc(800 + 64, GFP_KERNEL);
 	if (!result_avg || !buf) {
 		VERBOSE_SCALEOUT_ERRSTRING("out of memory");
 		goto oom_exit;
@@ -661,10 +663,7 @@ static int main_func(void *arg)
 	// Print the average of all experiments
 	SCALEOUT("END OF TEST. Calculating average duration per loop (nanoseconds)...\n");
 
-	buf[0] = 0;
-	strcat(buf, "\n");
-	strcat(buf, "Runs\tTime(ns)\n");
-
+	pr_alert("Runs\tTime(ns)\n");
 	for (exp = 0; exp < nruns; exp++) {
 		u64 avg;
 		u32 rem;
@@ -672,9 +671,13 @@ static int main_func(void *arg)
 		avg = div_u64_rem(result_avg[exp], 1000, &rem);
 		sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
 		strcat(buf, buf1);
+		if (strlen(buf) >= 800) {
+			pr_alert("%s", buf);
+			buf[0] = 0;
+		}
 	}
 
-	SCALEOUT("%s", buf);
+	pr_alert("%s", buf);
 
 oom_exit:
 	// This will shutdown everything including us.