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Message-ID: <e49f00c9-b9c8-a6a9-9595-6cedf5efe3e5@cn.fujitsu.com> Date: Sun, 24 Oct 2021 22:46:16 +0800 From: "Li, Zhijian" <lizhijian@...fujitsu.com> To: <paulmck@...nel.org> CC: <dave@...olabs.net>, <josh@...htriplett.org>, <rostedt@...dmis.org>, <mathieu.desnoyers@...icios.com>, <jiangshanlai@...il.com>, <joel@...lfernandes.org>, <rcu@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Philip Li <philip.li@...el.com>, "kernel test robot" <lkp@...el.com> 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 <philip.li@...el.com> >> Reported-by: kernel test robot <lkp@...el.com> >> Signed-off-by: Li Zhijian <lizhijian@...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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