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SubjectRe: [PATCH 2/2] refscale: prevent buffer to pr_alert() being too long
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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 <philip.li@intel.com>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> 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
>>
>>
>>
>


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