Re: [RFC PATCH] use snprintf instead of sprintf in rcu_torture_printk

From: Paul E. McKenney
Date: Thu Jun 19 2014 - 19:49:30 EST

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On Thu, Jun 19, 2014 at 07:24:48PM -0400, Pranith Kumar wrote:
> (dropping some CCs)
>
> On 06/19/2014 05:00 PM, Paul E. McKenney wrote:
> > On Wed, Jun 18, 2014 at 12:49:42PM -0700, Joe Perches wrote:
> >>
> >> I believe the function doesn't work well.
> >>
> >> static void
> >> rcu_torture_stats_print(void)
> >> {
> >> int size = nr_cpu_ids * 200 + 8192;
> >> char *buf;
> >>
> >> buf = kmalloc(size, GFP_KERNEL);
> >> if (!buf) {
> >> pr_err("rcu-torture: Out of memory, need: %d\n", size);
> >> return;
> >> }
> >> rcu_torture_printk(buf);
> >> pr_alert("%s", buf);
> >> kfree(buf);
> >> }
> >>
> >> rcu_torture_printk simply fills buf
> >>
> >> btw: I believe the arguments should pass size and
> >> rcu_torture_printk should use snprintf/size
> >>
> >> but all printks are limited to a maximum of 1024
> >> bytes so the large allocation is senseless and
> >> would even if it worked, would likely need to be
> >> vmalloc/vfree
> >
> > Fair point!
> >
> > Pranith, Romanov, if you would like part of RCU that is less touchy
> > about random hacking, this would be a good place to start. Scripts in
> > tools/testing/selftests/rcutorture/bin do care about some of the format,
> > but the variable-length portion generated by cur_ops->stats() is as far
> > as I know only parsed by human eyes.
> >
>
> Here is a first run of the change. Please let me know if I am totally off. RFC. :)

Thank you for taking this on!

> Three things on Todo list:
>
> * We need to check that we are using less than the allocated size of the buffer (used > size). (we are allocating a big buffer, so not sure if necessary)
> * Need to check with the scripts if they are working.
> * I used a loop for pr_alert(). I am not sure this is right, there should be a better way for printing large buffers
>
> If the overall structure is ok I will go ahead and check how the scripts are handling these changes.

One other thing... Convince this function (and a few others that it
calls) that the system really has 4096 CPUs, run this code, and see what
actually happens both before and after. Just to get a bit of practice
mixed in with the theory. ;-)

Thanx, Paul

> >From 0d52fdcd941b0eaaacb6732f59f609595ac14d11 Mon Sep 17 00:00:00 2001
> From: Pranith Kumar <bobby.prani@xxxxxxxxx>
> Date: Thu, 19 Jun 2014 19:00:46 -0400
> Subject: [PATCH 1/1] use snprintf instead of sprintf in rcu_torture_print_stats
>
> Signed-off-by: Pranith Kumar <bobby.prani@xxxxxxxxx>
> ---
> include/linux/torture.h | 2 +-
> kernel/rcu/rcutorture.c | 76 ++++++++++++++++++++++++++++---------------------
> kernel/torture.c | 7 +++--
> 3 files changed, 48 insertions(+), 37 deletions(-)
>
> diff --git a/include/linux/torture.h b/include/linux/torture.h
> index 5ca58fc..1e47ec7 100644
> --- a/include/linux/torture.h
> +++ b/include/linux/torture.h
> @@ -51,7 +51,7 @@
>
> /* Definitions for online/offline exerciser. */
> int torture_onoff_init(long ooholdoff, long oointerval);
> -char *torture_onoff_stats(char *page);
> +int torture_onoff_stats(char *page, int size);
> bool torture_onoff_failures(void);
>
> /* Low-rider random number generator. */
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 7fa34f8..f708db4 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -242,7 +242,7 @@ struct rcu_torture_ops {
> void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
> void (*cb_barrier)(void);
> void (*fqs)(void);
> - void (*stats)(char *page);
> + int (*stats)(char *page, int size);
> int irq_capable;
> int can_boost;
> const char *name;
> @@ -525,21 +525,22 @@ static void srcu_torture_barrier(void)
> srcu_barrier(&srcu_ctl);
> }
>
> -static void srcu_torture_stats(char *page)
> +static int srcu_torture_stats(char *page, int size)
> {
> - int cpu;
> + int cpu, used = 0;
> int idx = srcu_ctl.completed & 0x1;
>
> - page += sprintf(page, "%s%s per-CPU(idx=%d):",
> + used = snprintf(page, size, "%s%s per-CPU(idx=%d):",
> torture_type, TORTURE_FLAG, idx);
> for_each_possible_cpu(cpu) {
> long c0, c1;
>
> c0 = (long)per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx];
> c1 = (long)per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx];
> - page += sprintf(page, " %d(%ld,%ld)", cpu, c0, c1);
> + used += snprintf(page + used, size - used, " %d(%ld,%ld)", cpu, c0, c1);
> }
> - sprintf(page, "\n");
> + used += snprintf(page + used, size - used, "\n");
> + return used;
> }
>
> static void srcu_torture_synchronize_expedited(void)
> @@ -1033,10 +1034,10 @@ rcu_torture_reader(void *arg)
> /*
> * Create an RCU-torture statistics message in the specified buffer.
> */
> -static void
> -rcu_torture_printk(char *page)
> +static int
> +rcu_torture_printk(char *page, int size)
> {
> - int cpu;
> + int cpu, used = 0;
> int i;
> long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> @@ -1052,8 +1053,8 @@ rcu_torture_printk(char *page)
> if (pipesummary[i] != 0)
> break;
> }
> - page += sprintf(page, "%s%s ", torture_type, TORTURE_FLAG);
> - page += sprintf(page,
> + used += snprintf(page + used, size - used, "%s%s ", torture_type, TORTURE_FLAG);
> + used += snprintf(page + used, size - used,
> "rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
> rcu_torture_current,
> rcu_torture_current_version,
> @@ -1061,46 +1062,47 @@ rcu_torture_printk(char *page)
> atomic_read(&n_rcu_torture_alloc),
> atomic_read(&n_rcu_torture_alloc_fail),
> atomic_read(&n_rcu_torture_free));
> - page += sprintf(page, "rtmbe: %d rtbke: %ld rtbre: %ld ",
> + used += snprintf(page + used, size - used, "rtmbe: %d rtbke: %ld rtbre: %ld ",
> atomic_read(&n_rcu_torture_mberror),
> n_rcu_torture_boost_ktrerror,
> n_rcu_torture_boost_rterror);
> - page += sprintf(page, "rtbf: %ld rtb: %ld nt: %ld ",
> + used += snprintf(page + used, size - used, "rtbf: %ld rtb: %ld nt: %ld ",
> n_rcu_torture_boost_failure,
> n_rcu_torture_boosts,
> n_rcu_torture_timers);
> - page = torture_onoff_stats(page);
> - page += sprintf(page, "barrier: %ld/%ld:%ld",
> + used += torture_onoff_stats(page + used, size - used);
> + used += snprintf(page + used, size - used,
> + "barrier: %ld/%ld:%ld",
> n_barrier_successes,
> n_barrier_attempts,
> n_rcu_torture_barrier_error);
> - page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
> + used += snprintf(page + used, size - used, "\n%s%s ", torture_type, TORTURE_FLAG);
> if (atomic_read(&n_rcu_torture_mberror) != 0 ||
> n_rcu_torture_barrier_error != 0 ||
> n_rcu_torture_boost_ktrerror != 0 ||
> n_rcu_torture_boost_rterror != 0 ||
> n_rcu_torture_boost_failure != 0 ||
> i > 1) {
> - page += sprintf(page, "!!! ");
> + used += snprintf(page + used, size - used, "!!! ");
> atomic_inc(&n_rcu_torture_error);
> WARN_ON_ONCE(1);
> }
> - page += sprintf(page, "Reader Pipe: ");
> + used += snprintf(page + used, size - used, "Reader Pipe: ");
> for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
> - page += sprintf(page, " %ld", pipesummary[i]);
> - page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
> - page += sprintf(page, "Reader Batch: ");
> + used += snprintf(page + used, size - used, " %ld", pipesummary[i]);
> + used += snprintf(page + used, size - used, "\n%s%s ", torture_type, TORTURE_FLAG);
> + used += snprintf(page + used, size - used, "Reader Batch: ");
> for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
> - page += sprintf(page, " %ld", batchsummary[i]);
> - page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
> - page += sprintf(page, "Free-Block Circulation: ");
> + used += snprintf(page + used, size - used, " %ld", batchsummary[i]);
> + used += snprintf(page + used, size - used, "\n%s%s ", torture_type, TORTURE_FLAG);
> + used += snprintf(page + used, size - used, "Free-Block Circulation: ");
> for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
> - page += sprintf(page, " %d",
> + used += snprintf(page + used, size - used, " %d",
> atomic_read(&rcu_torture_wcount[i]));
> }
> - page += sprintf(page, "\n");
> + used += snprintf(page + used, size - used, "\n");
> if (cur_ops->stats)
> - cur_ops->stats(page);
> + used += cur_ops->stats(page, size - used);
> if (rtcv_snap == rcu_torture_current_version &&
> rcu_torture_current != NULL) {
> int __maybe_unused flags;
> @@ -1109,7 +1111,7 @@ rcu_torture_printk(char *page)
>
> rcutorture_get_gp_data(cur_ops->ttype,
> &flags, &gpnum, &completed);
> - page += sprintf(page,
> + used += snprintf(page + used, size - used,
> "??? Writer stall state %d g%lu c%lu f%#x\n",
> rcu_torture_writer_state,
> gpnum, completed, flags);
> @@ -1117,6 +1119,8 @@ rcu_torture_printk(char *page)
> rcutorture_trace_dump();
> }
> rtcv_snap = rcu_torture_current_version;
> +
> + return used;
> }
>
> /*
> @@ -1130,17 +1134,23 @@ rcu_torture_printk(char *page)
> static void
> rcu_torture_stats_print(void)
> {
> - int size = nr_cpu_ids * 200 + 8192;
> + int size = nr_cpu_ids * 200 + 8192, used = 0, size_pr;
> char *buf;
>
> - buf = kmalloc(size, GFP_KERNEL);
> + buf = vmalloc(size);
> if (!buf) {
> pr_err("rcu-torture: Out of memory, need: %d", size);
> return;
> }
> - rcu_torture_printk(buf);
> - pr_alert("%s", buf);
> - kfree(buf);
> + used = rcu_torture_printk(buf, size);
> +
> + /* printk can print only print LOG_LINE_MAX chars at a time */
> + while (used > 0) {
> + size_pr = pr_alert("%s", buf);
> + used -= size_pr;
> + buf += size_pr;
> + }
> + vfree(buf);
> }
>
> /*
> diff --git a/kernel/torture.c b/kernel/torture.c
> index 40bb511..da95335 100644
> --- a/kernel/torture.c
> +++ b/kernel/torture.c
> @@ -211,10 +211,11 @@ EXPORT_SYMBOL_GPL(torture_onoff_cleanup);
> /*
> * Print online/offline testing statistics.
> */
> -char *torture_onoff_stats(char *page)
> +int torture_onoff_stats(char *page, int size)
> {
> + int used = 0;
> #ifdef CONFIG_HOTPLUG_CPU
> - page += sprintf(page,
> + used = snprintf(page, size,
> "onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
> n_online_successes, n_online_attempts,
> n_offline_successes, n_offline_attempts,
> @@ -222,7 +223,7 @@ char *torture_onoff_stats(char *page)
> min_offline, max_offline,
> sum_online, sum_offline, HZ);
> #endif /* #ifdef CONFIG_HOTPLUG_CPU */
> - return page;
> + return used;
> }
> EXPORT_SYMBOL_GPL(torture_onoff_stats);
>
> --
> 1.9.1
>

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