linux-kernel - Re: [PATCH] fs, proc: Add start_data, end_data, start

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Date:	Sun, 11 Dec 2011 23:30:21 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Andrew Vagin <avagin@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Kees Cook <keescook@...omium.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs, proc: Add start_data, end_data, start_brk members to /proc/$pid/stat v2

Cyrill Gorcunov <gorcunov@...il.com> writes:

> On Wed, Dec 07, 2011 at 10:33:08AM +0400, Cyrill Gorcunov wrote:
>> 
>> No problem, I'll update (These segments are filled by binfmt handlers).
>> 
>
> This one should fit.

How extensively have you tested this.  I remember a few other occasions
where adding elements to a line in a proc file have resulted in breaking
readers.

I expect it is much safer to add this to /proc/<pid>/status rather than
/proc/<pid>/stat.

Eric


>
> 	Cyrill
> ---
> From: Cyrill Gorcunov <gorcunov@...nvz.org>
> Subject: [PATCH] fs, proc: Add start_data, end_data, start_brk members to /proc/$pid/stat v4
>
> These members are involved into calculation of program
> data segment (which might be seen in /proc/<pid>/statm)
> and into brk() call, so in a sake of restore we need
> these entries to be set exactly to the same value the
> process had at dumpimg time.
>
> While setting these entries back to a running task
> is supposed to be done via prctl interface (which is
> not addressed in this patch) the export of these values
> are done via /proc/$pid/stat, which already have start_code,
> end_code and start_stack entries.
>
> v2:
>  - Kees and Alexey pointed out that "1" hack is unnecessary,
>    so make it to have plain (mm && permitted) ? mm->member : 0
>    form.
>
> v3:
>  - Andrew pointed that documentation update is missed.
>    Chagelog is updated as well.
>
> v4:
>  - Update proc.txt to address concerns from Kees and Kame.
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Acked-by: Serge Hallyn <serge.hallyn@...onical.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> CC: Alexey Dobriyan <adobriyan@...il.com>
> ---
>  Documentation/filesystems/proc.txt |    3 +++
>  fs/proc/array.c                    |    7 +++++--
>  2 files changed, 8 insertions(+), 2 deletions(-)
>
> Index: linux-2.6.git/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux-2.6.git.orig/Documentation/filesystems/proc.txt
> +++ linux-2.6.git/Documentation/filesystems/proc.txt
> @@ -305,6 +305,9 @@ Table 1-4: Contents of the stat files (a
>    blkio_ticks   time spent waiting for block IO
>    gtime         guest time of the task in jiffies
>    cgtime        guest time of the task children in jiffies
> +  start_data    address above which program data+bss is placed
> +  end_data      address below which program data+bss is placed
> +  start_brk     address above which program heap can be expaned with brk() call
>  ..............................................................................
>  
>  The /proc/PID/maps file containing the currently mapped memory regions and
> Index: linux-2.6.git/fs/proc/array.c
> ===================================================================
> --- linux-2.6.git.orig/fs/proc/array.c
> +++ linux-2.6.git/fs/proc/array.c
> @@ -464,7 +464,7 @@ static int do_task_stat(struct seq_file
>  
>  	seq_printf(m, "%d (%s) %c %d %d %d %d %d %u %lu \
>  %lu %lu %lu %lu %lu %ld %ld %ld %ld %d 0 %llu %lu %ld %lu %lu %lu %lu %lu \
> -%lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu %lu %ld\n",
> +%lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu %lu %ld %lu %lu %lu\n",
>  		pid_nr_ns(pid, ns),
>  		tcomm,
>  		state,
> @@ -511,7 +511,10 @@ static int do_task_stat(struct seq_file
>  		task->policy,
>  		(unsigned long long)delayacct_blkio_ticks(task),
>  		cputime_to_clock_t(gtime),
> -		cputime_to_clock_t(cgtime));
> +		cputime_to_clock_t(cgtime),
> +		(mm && permitted) ? mm->start_data : 0,
> +		(mm && permitted) ? mm->end_data : 0,
> +		(mm && permitted) ? mm->start_brk : 0);
>  	if (mm)
>  		mmput(mm);
>  	return 0;
> --
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