From mboxrd@z Thu Jan  1 00:00:00 1970
From: gregkh@linuxfoundation.org (Greg KH)
Date: Thu, 4 Jun 2015 14:17:34 +0900
Subject: Change proc/<pid>/cmdline to 8k
In-Reply-To: <CAA=4087WKFH0K-dwL5DNY4TJJU=qYUcgHFBJavnAAZ3TZQUxaw@mail.gmail.com>
References: <CAA=4087WKFH0K-dwL5DNY4TJJU=qYUcgHFBJavnAAZ3TZQUxaw@mail.gmail.com>
Message-ID: <20150604051734.GA20983@kroah.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Thu, Jun 04, 2015 at 09:52:08AM +0530, Navin P wrote:
> Hi,
> 
>   I want to change the cmdline of a process to support 8096 . It works
> well on ppc where the page size is 65k.
>   But when i try to increase it on x86 (i686)
> 
> http://lxr.free-electrons.com/source/fs/proc/base.c  by doing
> 6*PAGE_SIZE, i get kernel panic after some time
> 
> 199 static int proc_pid_cmdline(struct seq_file *m, struct pid_namespace *ns,
> 200                             struct pid *pid, struct task_struct *task)
> 201 {
> 202         /*
> 203          * Rely on struct seq_operations::show() being called once
> 204          * per internal buffer allocation. See single_open(), traverse().
> 205          */
> 206         BUG_ON(m->size < PAGE_SIZE);
> 207         m->count += get_cmdline(task, m->buf, 6*PAGE_SIZE);
> 208         return 0;
> 209 }
> 210

That shows you that this will not work, sorry.