cpufreq: stats: Handle the case when trans_table goes beyond PAGE_SIZE

On platforms with large number of Pstates, the transition table, which
is a NxN matrix, can overflow beyond the PAGE_SIZE boundary.

This can be seen on POWER9 which has 100+ Pstates.

As a result, each time the trans_table is read for any of the CPUs, we
will get the following error.

---------------------------------------------------
fill_read_buffer: show+0x0/0xa0 returned bad count
---------------------------------------------------

This patch ensures that in case of an overflow, we print a warning
once in the dmesg and return FILE TOO LARGE error for this and all
subsequent accesses of trans_table.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index e75880eb037d..1e55b5790853 100644
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -118,8 +118,11 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
 			break;
 		len += snprintf(buf + len, PAGE_SIZE - len, "\n");
 	}
-	if (len >= PAGE_SIZE)
-		return PAGE_SIZE;
+
+	if (len >= PAGE_SIZE) {
+		pr_warn_once("cpufreq transition table exceeds PAGE_SIZE. Disabling\n");
+		return -EFBIG;
+	}
 	return len;
 }
 cpufreq_freq_attr_ro(trans_table);