linux-kernel - Re: [RFC 05/18] limits: track and present RLIMIT

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Date:	Mon, 13 Jun 2016 13:40:09 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	Topi Miettinen <toiwoton@...il.com>, linux-kernel@...r.kernel.org
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	John Stultz <john.stultz@...aro.org>,
	Janis Danisevskis <jdanis@...gle.com>,
	Calvin Owens <calvinowens@...com>, Jann Horn <jann@...jh.net>,
	"open list:FILESYSTEMS (VFS and infrastructure)" 
	<linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC 05/18] limits: track and present RLIMIT_NOFILE actual max

On 06/13/2016 12:44 PM, Topi Miettinen wrote:
> Track maximum number of files for the process, present current maximum
> in /proc/self/limits.

The core part should be its own patch.

Also, you have this weirdly named (and racy!) function bump_rlimit. 
Wouldn't this be nicer if you taught the rlimit code to track the 
*current* usage generically and to derive the max usage from that?

> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index a11eb71..227997b 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -630,8 +630,8 @@ static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
>  	/*
>  	 * print the file header
>  	 */
> -       seq_printf(m, "%-25s %-20s %-20s %-10s\n",
> -		  "Limit", "Soft Limit", "Hard Limit", "Units");
> +	seq_printf(m, "%-25s %-20s %-20s %-10s %-20s\n",
> +		   "Limit", "Soft Limit", "Hard Limit", "Units", "Max");

What existing programs, if any, does this break?

>
>  	for (i = 0; i < RLIM_NLIMITS; i++) {
>  		if (rlim[i].rlim_cur == RLIM_INFINITY)
> @@ -647,9 +647,11 @@ static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
>  			seq_printf(m, "%-20lu ", rlim[i].rlim_max);
>
>  		if (lnames[i].unit)
> -			seq_printf(m, "%-10s\n", lnames[i].unit);
> +			seq_printf(m, "%-10s", lnames[i].unit);
>  		else
> -			seq_putc(m, '\n');
> +			seq_printf(m, "%-10s", "");
> +		seq_printf(m, "%-20lu\n",
> +			   task->signal->rlim_curmax[i]);
>  	}
>
>  	return 0;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 9c48a08..0150380 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -782,6 +782,7 @@ struct signal_struct {
>  	 * have no need to disable irqs.
>  	 */
>  	struct rlimit rlim[RLIM_NLIMITS];
> +	unsigned long rlim_curmax[RLIM_NLIMITS];
>
>  #ifdef CONFIG_BSD_PROCESS_ACCT
>  	struct pacct_struct pacct;	/* per-process accounting information */
> @@ -3376,6 +3377,12 @@ static inline unsigned long rlimit_max(unsigned int limit)
>  	return task_rlimit_max(current, limit);
>  }
>
> +static inline void bump_rlimit(unsigned int limit, unsigned long r)
> +{
> +	if (READ_ONCE(current->signal->rlim_curmax[limit]) < r)
> +		current->signal->rlim_curmax[limit] = r;
> +}
> +
>  #ifdef CONFIG_CPU_FREQ
>  struct update_util_data {
>  	void (*func)(struct update_util_data *data,
>