refscale: Prevent buffer to pr_alert() being too long

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>

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index b59457cef88d52c742ad86398233105eaed6abf9..d8ed1ca3adc0480c32c6fadf8d5944cda5aaf76f 100644 (file)
--- 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.