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 <[email protected]> Acked-by: Viresh Kumar <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]>
ambv · Nov 8, 2017 · f7bc9b2 · f7bc9b2
1 parent 0011c6d
commit f7bc9b2
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diff --git a/Documentation/cpu-freq/cpufreq-stats.txt b/Documentation/cpu-freq/cpufreq-stats.txt
@@ -90,6 +90,9 @@ Freq_i to Freq_j. Freq_i is in descending order with increasing rows and
 Freq_j is in descending order with increasing columns. The output here also 
 contains the actual freq values for each row and column for better readability.
 
+If the transition table is bigger than PAGE_SIZE, reading this will
+return an -EFBIG error.
+
 --------------------------------------------------------------------------------
 <mysystem>:/sys/devices/system/cpu/cpu0/cpufreq/stats # cat trans_table
    From  :    To

diff --git 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);