2021-10-22 10:53:39

by Li Zhijian

Subject: [PATCH 2/2] refscale: prevent buffer to pr_alert() being too long

0Day/LKP observed that the refscale results become incompleted
when a larger nruns(such as 300) is specified.
It seems that printk() can accept < 1024 buffer at once.
Print the buffer if its length exceeds 800 simply.

CC: Philip Li <[email protected]>
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Li Zhijian <[email protected]>
---
kernel/rcu/refscale.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 2cbe2a2ba387..b1b9052010fd 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -604,7 +604,7 @@ static u64 process_durations(int n)
char *buf;
u64 sum = 0;

- buf = kmalloc(128 + nreaders * 32, GFP_KERNEL);
+ buf = kmalloc(64 * 20, GFP_KERNEL);
if (!buf)
return 0;
buf[0] = 0;
@@ -617,13 +617,15 @@ static u64 process_durations(int n)

if (i % 5 == 0)
strcat(buf, "\n");
+ if (strlen(buf) > 800) {
+ pr_alert("%s", buf);
+ buf[0] = 0;
+ }
strcat(buf, buf1);

sum += rt->last_duration_ns;
}
- strcat(buf, "\n");
-
- SCALEOUT("%s\n", buf);
+ pr_alert("%s\n", buf);

kfree(buf);
return sum;
@@ -648,7 +650,7 @@ static int main_func(void *arg)

VERBOSE_SCALEOUT("main_func task started");
result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL);
- buf = kzalloc(64 + nruns * 32, GFP_KERNEL);
+ buf = kzalloc(64 * 20, GFP_KERNEL);
if (!result_avg || !buf) {
VERBOSE_SCALEOUT_ERRSTRING("out of memory");
errexit = true;
@@ -701,10 +703,7 @@ static int main_func(void *arg)
if (errexit)
goto err;

- buf[0] = 0;
- strcat(buf, "\n");
- strcat(buf, "Runs\tTime(ns)\n");
-
+ pr_alert("Runs\tTime(ns)\n");
for (exp = 0; exp < nruns; exp++) {
u64 avg;
u32 rem;
@@ -712,9 +711,13 @@ static int main_func(void *arg)
avg = div_u64_rem(result_avg[exp], 1000, &rem);
sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
strcat(buf, buf1);
+ if (strlen(buf) > 800) {
+ pr_alert("%s", buf);
+ buf[0] = 0;
+ }
}

- SCALEOUT("%s", buf);
+ pr_alert("%s", buf);

err:
// This will shutdown everything including us.
--
2.33.0

2021-10-22 23:20:28

by Paul E. McKenney

Subject: Re: [PATCH 2/2] refscale: prevent buffer to pr_alert() being too long

On Fri, Oct 22, 2021 at 06:51:11PM +0800, Li Zhijian wrote:
> 0Day/LKP observed that the refscale results become incompleted
> when a larger nruns(such as 300) is specified.
> It seems that printk() can accept < 1024 buffer at once.
> Print the buffer if its length exceeds 800 simply.
>
> CC: Philip Li <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Signed-off-by: Li Zhijian <[email protected]>

Good catch! A couple of questions below.

Thanx, Paul

> ---
> kernel/rcu/refscale.c | 23 +++++++++++++----------
> 1 file changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
> index 2cbe2a2ba387..b1b9052010fd 100644
> --- a/kernel/rcu/refscale.c
> +++ b/kernel/rcu/refscale.c
> @@ -604,7 +604,7 @@ static u64 process_durations(int n)
> char *buf;
> u64 sum = 0;
>
> - buf = kmalloc(128 + nreaders * 32, GFP_KERNEL);
> + buf = kmalloc(64 * 20, GFP_KERNEL);

This allocation (and the one below) is 1280 bytes rather than
1024 bytes. Why the extra couple hundred bytes?

> if (!buf)
> return 0;
> buf[0] = 0;
> @@ -617,13 +617,15 @@ static u64 process_durations(int n)
>
> if (i % 5 == 0)
> strcat(buf, "\n");
> + if (strlen(buf) > 800) {
> + pr_alert("%s", buf);

Does the tools/testing/selftests/rcutorture/bin/kvm-recheck-refscale.sh
script also require changes to handle the partial lines?

Same for the later comparison against 800.

> + buf[0] = 0;
> + }
> strcat(buf, buf1);
>
> sum += rt->last_duration_ns;
> }
> - strcat(buf, "\n");
> -
> - SCALEOUT("%s\n", buf);
> + pr_alert("%s\n", buf);
>
> kfree(buf);
> return sum;
> @@ -648,7 +650,7 @@ static int main_func(void *arg)
>
> VERBOSE_SCALEOUT("main_func task started");
> result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL);
> - buf = kzalloc(64 + nruns * 32, GFP_KERNEL);
> + buf = kzalloc(64 * 20, GFP_KERNEL);
> if (!result_avg || !buf) {
> VERBOSE_SCALEOUT_ERRSTRING("out of memory");
> errexit = true;
> @@ -701,10 +703,7 @@ static int main_func(void *arg)
> if (errexit)
> goto err;
>
> - buf[0] = 0;
> - strcat(buf, "\n");
> - strcat(buf, "Runs\tTime(ns)\n");
> -
> + pr_alert("Runs\tTime(ns)\n");
> for (exp = 0; exp < nruns; exp++) {
> u64 avg;
> u32 rem;
> @@ -712,9 +711,13 @@ static int main_func(void *arg)
> avg = div_u64_rem(result_avg[exp], 1000, &rem);
> sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
> strcat(buf, buf1);
> + if (strlen(buf) > 800) {
> + pr_alert("%s", buf);
> + buf[0] = 0;
> + }
> }
>
> - SCALEOUT("%s", buf);
> + pr_alert("%s", buf);
>
> err:
> // This will shutdown everything including us.
> --
> 2.33.0
>
>
>

2021-10-24 14:55:52

by Li Zhijian

Subject: Re: [PATCH 2/2] refscale: prevent buffer to pr_alert() being too long

on 2021/10/23 7:15, Paul E. McKenney wrote:
> On Fri, Oct 22, 2021 at 06:51:11PM +0800, Li Zhijian wrote:
>> 0Day/LKP observed that the refscale results become incompleted
>> when a larger nruns(such as 300) is specified.
>> It seems that printk() can accept < 1024 buffer at once.
>> Print the buffer if its length exceeds 800 simply.
>>
>> CC: Philip Li <[email protected]>
>> Reported-by: kernel test robot <[email protected]>
>> Signed-off-by: Li Zhijian <[email protected]>
> Good catch! A couple of questions below.
>
> Thanx, Paul
>
>> ---
>> kernel/rcu/refscale.c | 23 +++++++++++++----------
>> 1 file changed, 13 insertions(+), 10 deletions(-)
>>
>> diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
>> index 2cbe2a2ba387..b1b9052010fd 100644
>> --- a/kernel/rcu/refscale.c
>> +++ b/kernel/rcu/refscale.c
>> @@ -604,7 +604,7 @@ static u64 process_durations(int n)
>> char *buf;
>> u64 sum = 0;
>>
>> - buf = kmalloc(128 + nreaders * 32, GFP_KERNEL);
>> + buf = kmalloc(64 * 20, GFP_KERNEL);
> This allocation (and the one below) is 1280 bytes rather than
> 1024 bytes. Why the extra couple hundred bytes?

Nothing special, so let's change 1024 or (800 + 64 ),which is sufficent as well ?


>
>> if (!buf)
>> return 0;
>> buf[0] = 0;
>> @@ -617,13 +617,15 @@ static u64 process_durations(int n)
>>
>> if (i % 5 == 0)
>> strcat(buf, "\n");
>> + if (strlen(buf) > 800) {
>> + pr_alert("%s", buf);
> Does the tools/testing/selftests/rcutorture/bin/kvm-recheck-refscale.sh
> script also require changes to handle the partial lines?

I missed that, i will take a look at it

Thanks

Zhijian


>
> Same for the later comparison against 800.
>
>> + buf[0] = 0;
>> + }
>> strcat(buf, buf1);
>>
>> sum += rt->last_duration_ns;
>> }
>> - strcat(buf, "\n");
>> -
>> - SCALEOUT("%s\n", buf);
>> + pr_alert("%s\n", buf);
>>
>> kfree(buf);
>> return sum;
>> @@ -648,7 +650,7 @@ static int main_func(void *arg)
>>
>> VERBOSE_SCALEOUT("main_func task started");
>> result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL);
>> - buf = kzalloc(64 + nruns * 32, GFP_KERNEL);
>> + buf = kzalloc(64 * 20, GFP_KERNEL);
>> if (!result_avg || !buf) {
>> VERBOSE_SCALEOUT_ERRSTRING("out of memory");
>> errexit = true;
>> @@ -701,10 +703,7 @@ static int main_func(void *arg)
>> if (errexit)
>> goto err;
>>
>> - buf[0] = 0;
>> - strcat(buf, "\n");
>> - strcat(buf, "Runs\tTime(ns)\n");
>> -
>> + pr_alert("Runs\tTime(ns)\n");
>> for (exp = 0; exp < nruns; exp++) {
>> u64 avg;
>> u32 rem;
>> @@ -712,9 +711,13 @@ static int main_func(void *arg)
>> avg = div_u64_rem(result_avg[exp], 1000, &rem);
>> sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
>> strcat(buf, buf1);
>> + if (strlen(buf) > 800) {
>> + pr_alert("%s", buf);
>> + buf[0] = 0;
>> + }
>> }
>>
>> - SCALEOUT("%s", buf);
>> + pr_alert("%s", buf);
>>
>> err:
>> // This will shutdown everything including us.
>> --
>> 2.33.0
>>
>>
>>
>

2021-10-24 23:23:37

by Paul E. McKenney

Subject: Re: [PATCH 2/2] refscale: prevent buffer to pr_alert() being too long

On Sun, Oct 24, 2021 at 10:46:16PM +0800, Li, Zhijian wrote:
>
> on 2021/10/23 7:15, Paul E. McKenney wrote:
> > On Fri, Oct 22, 2021 at 06:51:11PM +0800, Li Zhijian wrote:
> > > 0Day/LKP observed that the refscale results become incompleted
> > > when a larger nruns(such as 300) is specified.
> > > It seems that printk() can accept < 1024 buffer at once.
> > > Print the buffer if its length exceeds 800 simply.
> > >
> > > CC: Philip Li <[email protected]>
> > > Reported-by: kernel test robot <[email protected]>
> > > Signed-off-by: Li Zhijian <[email protected]>
> > Good catch! A couple of questions below.
> >
> > Thanx, Paul
> >
> > > ---
> > > kernel/rcu/refscale.c | 23 +++++++++++++----------
> > > 1 file changed, 13 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
> > > index 2cbe2a2ba387..b1b9052010fd 100644
> > > --- a/kernel/rcu/refscale.c
> > > +++ b/kernel/rcu/refscale.c
> > > @@ -604,7 +604,7 @@ static u64 process_durations(int n)
> > > char *buf;
> > > u64 sum = 0;
> > > - buf = kmalloc(128 + nreaders * 32, GFP_KERNEL);
> > > + buf = kmalloc(64 * 20, GFP_KERNEL);
> > This allocation (and the one below) is 1280 bytes rather than
> > 1024 bytes. Why the extra couple hundred bytes?
>
> Nothing special, so let's change 1024 or (800 + 64 ),which is sufficent as well ?

Either works. No problem having a few extra bytes, but 200 seemed a bit
excessive. ;-)

> > > if (!buf)
> > > return 0;
> > > buf[0] = 0;
> > > @@ -617,13 +617,15 @@ static u64 process_durations(int n)
> > > if (i % 5 == 0)
> > > strcat(buf, "\n");
> > > + if (strlen(buf) > 800) {
> > > + pr_alert("%s", buf);
> > Does the tools/testing/selftests/rcutorture/bin/kvm-recheck-refscale.sh
> > script also require changes to handle the partial lines?
>
> I missed that, i will take a look at it

Looking forward to seeing what you come up with.

Thanx, Paul

> Thanks
>
> Zhijian
>
>
> >
> > Same for the later comparison against 800.
> >
> > > + buf[0] = 0;
> > > + }
> > > strcat(buf, buf1);
> > > sum += rt->last_duration_ns;
> > > }
> > > - strcat(buf, "\n");
> > > -
> > > - SCALEOUT("%s\n", buf);
> > > + pr_alert("%s\n", buf);
> > > kfree(buf);
> > > return sum;
> > > @@ -648,7 +650,7 @@ static int main_func(void *arg)
> > > VERBOSE_SCALEOUT("main_func task started");
> > > result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL);
> > > - buf = kzalloc(64 + nruns * 32, GFP_KERNEL);
> > > + buf = kzalloc(64 * 20, GFP_KERNEL);
> > > if (!result_avg || !buf) {
> > > VERBOSE_SCALEOUT_ERRSTRING("out of memory");
> > > errexit = true;
> > > @@ -701,10 +703,7 @@ static int main_func(void *arg)
> > > if (errexit)
> > > goto err;
> > > - buf[0] = 0;
> > > - strcat(buf, "\n");
> > > - strcat(buf, "Runs\tTime(ns)\n");
> > > -
> > > + pr_alert("Runs\tTime(ns)\n");
> > > for (exp = 0; exp < nruns; exp++) {
> > > u64 avg;
> > > u32 rem;
> > > @@ -712,9 +711,13 @@ static int main_func(void *arg)
> > > avg = div_u64_rem(result_avg[exp], 1000, &rem);
> > > sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
> > > strcat(buf, buf1);
> > > + if (strlen(buf) > 800) {
> > > + pr_alert("%s", buf);
> > > + buf[0] = 0;
> > > + }
> > > }
> > > - SCALEOUT("%s", buf);
> > > + pr_alert("%s", buf);
> > > err:
> > > // This will shutdown everything including us.
> > > --
> > > 2.33.0
> > >
> > >
> > >
> >
>
>

2021-10-25 03:40:08

by Zhijian Li (Fujitsu)

Subject: Re: [PATCH 2/2] refscale: prevent buffer to pr_alert() being too long

On 25/10/2021 06:56, Paul E. McKenney wrote:
>
>>>> if (!buf)
>>>> return 0;
>>>> buf[0] = 0;
>>>> @@ -617,13 +617,15 @@ static u64 process_durations(int n)
>>>> if (i % 5 == 0)
>>>> strcat(buf, "\n");
>>>> + if (strlen(buf) > 800) {
>>>> + pr_alert("%s", buf);
>>> Does the tools/testing/selftests/rcutorture/bin/kvm-recheck-refscale.sh
>>> script also require changes to handle the partial lines?
Looks it doesn't matter for kvm-recheck-refscale.sh where it will not check these output.


>>>> u32 rem;
>>>> @@ -712,9 +711,13 @@ static int main_func(void *arg)
>>>> avg = div_u64_rem(result_avg[exp], 1000, &rem);
>>>> sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem);
>>>> strcat(buf, buf1);
>>>> + if (strlen(buf) > 800) {
>>>> + pr_alert("%s", buf);
>>>> + buf[0] = 0;
>>>> + }
>>>> }
>>>> - SCALEOUT("%s", buf);
>>>> + pr_alert("%s", buf);
it will not introduce partial lines here, buf  is always ended with '\n'

I have checked the regexp in tools/testing/selftests/rcutorture/bin/kvm-recheck-refscale.sh
and verify it with the new result, it always works.


Thanks
Zhijian



>>>> err:
>>>> // This will shutdown everything including us.
>>>> --
>>>> 2.33.0
>>>>
>>>>
>>>>
>>
>