Re: [PATCH v2] kernel/rcutorture.c: be sure of enough memory forresult printing

[Paul E. McKenney]

On Thu, Nov 07, 2013 at 10:30:25AM +0800, Chen Gang wrote:
> If the contents is more than 4096 bytes (e.g. if have 1K cpus), current
> sprintf() will cause memory overflow. And this fix patch is to be sure
> of memory large enough.
> 
> Benefit:
> 
>  - do not truncate printing contents.
>  - extensible, it is large enough for printing various related contents.
>  - simple and clear enough for both source code readers and writers.
> 
> Shortcoming:
> 
>  - It will waste some memory:
> 
>     1 cpu now comsumes 50 - 60 bytes, and this patch provides 200 bytes.
>     global printing now comsumes a few KB, and this patch provide 8KB,
>     so for 1K cpus, it may waste 100 - 200 KB memory.
> 
>    after finish printing, it will free the related memory, quickly.
>    it is a test module, so wast a little memory for extensible is OK.
> 
> Related  test (Fedora16 2 CPUs, 2GB RAM x86_64)
> 
>  - as module, with/without "torture_type=srcu".
>  - build-in not boot runnable, with/without "torture_type=srcu".
>  - build-in let boot runnable, with/without "torture_type=srcu".
> 
> 
> Signed-off-by: Chen Gang <gang.chen@xxxxxxxxxxx>

Thank you, queued for 3.14.

							Thanx, Paul

> ---
>  kernel/rcu/torture.c |   68 +++++++++++++++++++++++++------------------------
>  1 files changed, 35 insertions(+), 33 deletions(-)
> 
> diff --git a/kernel/rcu/torture.c b/kernel/rcu/torture.c
> index 3929cd4..a60874c 100644
> --- a/kernel/rcu/torture.c
> +++ b/kernel/rcu/torture.c
> @@ -139,8 +139,6 @@ MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");
>  #define VERBOSE_PRINTK_ERRSTRING(s) \
>  	do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0)
> 
> -static char printk_buf[4096];
> -
>  static int nrealreaders;
>  static struct task_struct *writer_task;
>  static struct task_struct **fakewriter_tasks;
> @@ -376,7 +374,7 @@ struct rcu_torture_ops {
>  	void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
>  	void (*cb_barrier)(void);
>  	void (*fqs)(void);
> -	int (*stats)(char *page);
> +	void (*stats)(char *page);
>  	int irq_capable;
>  	int can_boost;
>  	const char *name;
> @@ -578,21 +576,19 @@ static void srcu_torture_barrier(void)
>  	srcu_barrier(&srcu_ctl);
>  }
> 
> -static int srcu_torture_stats(char *page)
> +static void srcu_torture_stats(char *page)
>  {
> -	int cnt = 0;
>  	int cpu;
>  	int idx = srcu_ctl.completed & 0x1;
> 
> -	cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
> +	page += sprintf(page, "%s%s per-CPU(idx=%d):",
>  		       torture_type, TORTURE_FLAG, idx);
>  	for_each_possible_cpu(cpu) {
> -		cnt += sprintf(&page[cnt], " %d(%lu,%lu)", cpu,
> +		page += sprintf(page, " %d(%lu,%lu)", cpu,
>  			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
>  			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
>  	}
> -	cnt += sprintf(&page[cnt], "\n");
> -	return cnt;
> +	sprintf(page, "\n");
>  }
> 
>  static void srcu_torture_synchronize_expedited(void)
> @@ -1052,10 +1048,9 @@ rcu_torture_reader(void *arg)
>  /*
>   * Create an RCU-torture statistics message in the specified buffer.
>   */
> -static int
> +static void
>  rcu_torture_printk(char *page)
>  {
> -	int cnt = 0;
>  	int cpu;
>  	int i;
>  	long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
> @@ -1071,8 +1066,8 @@ rcu_torture_printk(char *page)
>  		if (pipesummary[i] != 0)
>  			break;
>  	}
> -	cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);
> -	cnt += sprintf(&page[cnt],
> +	page += sprintf(page, "%s%s ", torture_type, TORTURE_FLAG);
> +	page += sprintf(page,
>  		       "rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
>  		       rcu_torture_current,
>  		       rcu_torture_current_version,
> @@ -1080,53 +1075,52 @@ rcu_torture_printk(char *page)
>  		       atomic_read(&n_rcu_torture_alloc),
>  		       atomic_read(&n_rcu_torture_alloc_fail),
>  		       atomic_read(&n_rcu_torture_free));
> -	cnt += sprintf(&page[cnt], "rtmbe: %d rtbke: %ld rtbre: %ld ",
> +	page += sprintf(page, "rtmbe: %d rtbke: %ld rtbre: %ld ",
>  		       atomic_read(&n_rcu_torture_mberror),
>  		       n_rcu_torture_boost_ktrerror,
>  		       n_rcu_torture_boost_rterror);
> -	cnt += sprintf(&page[cnt], "rtbf: %ld rtb: %ld nt: %ld ",
> +	page += sprintf(page, "rtbf: %ld rtb: %ld nt: %ld ",
>  		       n_rcu_torture_boost_failure,
>  		       n_rcu_torture_boosts,
>  		       n_rcu_torture_timers);
> -	cnt += sprintf(&page[cnt],
> +	page += sprintf(page,
>  		       "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,
>  		       min_online, max_online,
>  		       min_offline, max_offline,
>  		       sum_online, sum_offline, HZ);
> -	cnt += sprintf(&page[cnt], "barrier: %ld/%ld:%ld",
> +	page += sprintf(page, "barrier: %ld/%ld:%ld",
>  		       n_barrier_successes,
>  		       n_barrier_attempts,
>  		       n_rcu_torture_barrier_error);
> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
> +	page += sprintf(page, "\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) {
> -		cnt += sprintf(&page[cnt], "!!! ");
> +		page += sprintf(page, "!!! ");
>  		atomic_inc(&n_rcu_torture_error);
>  		WARN_ON_ONCE(1);
>  	}
> -	cnt += sprintf(&page[cnt], "Reader Pipe: ");
> +	page += sprintf(page, "Reader Pipe: ");
>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
> -		cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);
> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
> -	cnt += sprintf(&page[cnt], "Reader Batch: ");
> +		page += sprintf(page, " %ld", pipesummary[i]);
> +	page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
> +	page += sprintf(page, "Reader Batch: ");
>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
> -		cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);
> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
> -	cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
> +		page += sprintf(page, " %ld", batchsummary[i]);
> +	page += sprintf(page, "\n%s%s ", torture_type, TORTURE_FLAG);
> +	page += sprintf(page, "Free-Block Circulation: ");
>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
> -		cnt += sprintf(&page[cnt], " %d",
> +		page += sprintf(page, " %d",
>  			       atomic_read(&rcu_torture_wcount[i]));
>  	}
> -	cnt += sprintf(&page[cnt], "\n");
> +	page += sprintf(page, "\n");
>  	if (cur_ops->stats)
> -		cnt += cur_ops->stats(&page[cnt]);
> -	return cnt;
> +		cur_ops->stats(page);
>  }
> 
>  /*
> @@ -1140,10 +1134,18 @@ rcu_torture_printk(char *page)
>  static void
>  rcu_torture_stats_print(void)
>  {
> -	int cnt;
> +	int size = nr_cpu_ids * 200 + 8192; /* be sure of large enough */
> +	char *buf;
> 
> -	cnt = rcu_torture_printk(printk_buf);
> -	pr_alert("%s", printk_buf);
> +	buf = kmalloc(size, GFP_KERNEL);
> +	if (!buf) {
> +		pr_err("rcu-torture: no enough memory for printing, requre: %d",
> +			size);
> +		return;
> +	}
> +	rcu_torture_printk(buf);
> +	pr_alert("%s", buf);
> +	kfree(buf);
>  }
> 
>  /*
> -- 
> 1.7.7.6
> 

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