| Message ID | 1510032157-31857-1-git-send-email-ego@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On 07-11-17, 10:52, Gautham R. Shenoy wrote: > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> > > 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 <ego@linux.vnet.ibm.com> > --- > 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. > + > -------------------------------------------------------------------------------- > <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 > 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.
Hi Viresh, On Tue, Nov 07, 2017 at 11:02:36AM +0530, Viresh Kumar wrote: > On 07-11-17, 10:52, Gautham R. Shenoy wrote: > > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> > > > > 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/ Will fix this. > > > error. The subsequent reads also return FILE TOO LARGE error. > > > > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> > > --- > > 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. > > + > > -------------------------------------------------------------------------------- > > <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 > > 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. Sure, I see what you mean. I can change the warning below to a pr_warn_once, so that the dmesg isn't cluttered everytime someone reads the trans_table. > > > 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. Ok. Will resend the patch incorporating your suggestions. Thanks for the review. > > -- > viresh >
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. + -------------------------------------------------------------------------------- <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 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; 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; + 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; + } return len; } cpufreq_freq_attr_ro(trans_table);