linux-kernel - [PATCH rcu 05/17] refscale: Prevent buffer to pr

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Date:   Wed,  1 Dec 2021 16:43:24 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        Li Zhijian <lizhijian@...fujitsu.com>,
        Philip Li <philip.li@...el.com>,
        kernel test robot <lkp@...el.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 05/17] refscale: Prevent buffer to pr_alert() being too long

From: Li Zhijian <lizhijian@...fujitsu.com>

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@...el.com>
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Li Zhijian <lizhijian@...fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 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 b59457cef88d5..d8ed1ca3adc04 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -604,7 +604,7 @@ 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;
@@ -617,13 +617,15 @@ 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;
@@ -647,7 +649,7 @@ 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;
@@ -695,10 +697,7 @@ 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;
@@ -706,9 +705,13 @@ 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.
-- 
2.31.1.189.g2e36527f23