On Thu, May 28, 2015 at 12:49:53AM +0300, Alexey Dobriyan wrote:
...
> -static int proc_pid_cmdline(struct seq_file *m, struct pid_namespace *ns,
> - struct pid *pid, struct task_struct *task)
> +static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
> + size_t _count, loff_t *pos)
> {
> + struct task_struct *tsk;
> + struct mm_struct *mm;
> + char *page;
> + unsigned long count = _count;
> + unsigned long arg_start, arg_end, env_start, env_end;
> + unsigned long len1, len2, len;
> + unsigned long p;
> + char c;
> + ssize_t rv;
> +
> + BUG_ON(*pos < 0);
> +
> + tsk = get_proc_task(file_inode(file));
> + if (!tsk)
> + return -ESRCH;
> + mm = get_task_mm(tsk);
> + put_task_struct(tsk);
> + if (!mm)
> + return 0;
> + /* Check if process spawned far enough to have cmdline. */
> + if (!mm->env_end) {
> + rv = 0;
> + goto out_mmput;
> + }
> +
> + page = (char *)__get_free_page(GFP_TEMPORARY);
> + if (!page) {
> + rv = -ENOMEM;
> + goto out_mmput;
> + }
> +
> + down_read(&mm->mmap_sem);
> + arg_start = mm->arg_start;
> + arg_end = mm->arg_end;
> + env_start = mm->env_start;
> + env_end = mm->env_end;
> + up_read(&mm->mmap_sem);
Could you please explain why this down/up is needed?
(the rest is hard to review at night :)
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