From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH] cpufreq:stats: Handle the case when trans_table goes beyond PAGE_SIZE Date: Tue, 7 Nov 2017 11:02:36 +0530 Message-ID: <20171107053236.GA3297@vireshk-i7> References: <1510032157-31857-1-git-send-email-ego@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pf0-f194.google.com ([209.85.192.194]:55688 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752791AbdKGFck (ORCPT ); Tue, 7 Nov 2017 00:32:40 -0500 Received: by mail-pf0-f194.google.com with SMTP id 17so9508310pfn.12 for ; Mon, 06 Nov 2017 21:32:39 -0800 (PST) Content-Disposition: inline In-Reply-To: <1510032157-31857-1-git-send-email-ego@linux.vnet.ibm.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Gautham R. Shenoy" Cc: "Rafael J . Wysocki" , Akshay Adiga , shilpa.bhat@linux.vnet.ibm.com, Vaidyanathan Srinivasan , linux-pm@vger.kernel.org On 07-11-17, 10:52, Gautham R. Shenoy wrote: > From: "Gautham R. Shenoy" > > 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 detect the overflow the first time the trans_table is read > and print a warning in the dmesg and return return the FILE TOO LARGE s/return return/return/ > error. The subsequent reads also return FILE TOO LARGE error. > > Signed-off-by: Gautham R. Shenoy > --- > Documentation/cpu-freq/cpufreq-stats.txt | 3 +++ > drivers/cpufreq/cpufreq_stats.c | 11 +++++++++-- > 2 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/Documentation/cpu-freq/cpufreq-stats.txt b/Documentation/cpu-freq/cpufreq-stats.txt > index 2bbe207..a873855 100644 > --- 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. > + > -------------------------------------------------------------------------------- > :/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 > index e75880e..3cb717c 100644 > --- a/drivers/cpufreq/cpufreq_stats.c > +++ b/drivers/cpufreq/cpufreq_stats.c > @@ -79,6 +79,7 @@ static ssize_t store_reset(struct cpufreq_policy *policy, const char *buf, > return count; > } > > +bool trans_table_overflow; This should be marked static and would be better to move it as local to below function, but ... > static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf) > { > struct cpufreq_stats *stats = policy->stats; > @@ -88,6 +89,9 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf) > if (policy->fast_switch_enabled) > return 0; > > + if (unlikely(trans_table_overflow)) > + return -EFBIG; > + Do we really need to optimize this path at all? This is debug stuff really. Over that a person can theoretically rmmod the driver, insmod another driver and the problem may go away then. And so above would be problematic then. > len += snprintf(buf + len, PAGE_SIZE - len, " From : To\n"); > len += snprintf(buf + len, PAGE_SIZE - len, " : "); > for (i = 0; i < stats->state_num; i++) { > @@ -118,8 +122,11 @@ 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) { > + trans_table_overflow = true; > + pr_warn("cpufreq transition table exceeds PAGE_SIZE. Disabling\n"); > + return -EFBIG; > + } I would suggest making only this change and removing other optimizations completely. -- viresh