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Commit f7bc9b20 authored by Gautham R. Shenoy's avatar Gautham R. Shenoy Committed by Rafael J. Wysocki
Browse files

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: default avatarGautham R. Shenoy <ego@linux.vnet.ibm.com>
Acked-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 0011c6da

Documentation/cpu-freq/cpufreq-stats.txt

+3 −0
Original line number Diff line number Diff line
@@ -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

drivers/cpufreq/cpufreq_stats.c

+5 −2
Original line number Diff line number Diff line
@@ -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);