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

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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.

Change-Id: I4d22a81fcad037e887b4ddf2999904b321401441
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>
Git-repo: https://android.googlesource.com/kernel/common/
Git-commit: f7bc9b209e27c0b617378400136cc663a6314d0c
Signed-off-by: Rahul Shahare <rshaha@codeaurora.org>
This commit is contained in:
Gautham R. Shenoy 2017-11-07 13:39:29 +05:30 committed by Rahul Shahare
parent c81bd9708c
commit 39174fe35f
2 changed files with 8 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/cpu-freq/cpufreq-stats.txt
View File

@ -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

7
drivers/cpufreq/cpufreq_stats.c
View File

@ -113,8 +113,11 @@ 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);