Re: [PACTH v1] mm, proc: Implement /proc/<pid>/totmaps

From: Robert Foss
Date: Wed Aug 10 2016 - 14:22:52 EST




On 2016-08-10 11:42 AM, Mateusz Guzik wrote:
On Wed, Aug 10, 2016 at 11:39:12AM -0400, Robert Foss wrote:


On 2016-08-09 04:17 PM, Robert Foss wrote:
+static int totmaps_proc_show(struct seq_file *m, void *data)
+{
+ struct proc_maps_private *priv = m->private;
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ struct mem_size_stats *mss_sum = priv->mss;
+
+ /* reference to priv->task already taken */
+ /* but need to get the mm here because */
+ /* task could be in the process of exiting */
+ mm = get_task_mm(priv->task);
+ if (!mm || IS_ERR(mm))
+ return -EINVAL;
+

That's not how it's done in smaps.

Alright, I'll have to look into the difference between this approach and
the smaps one.


I had a look at show_smaps(), and it's not entirely clear to me what the
advantage of doing it show_smaps() way.

mm = get_task_mm(priv->task) is needed to iterate through all of the
mappings. Is there a preferable way of doing that?

In the other part of the mail I stated smaps goes to proc_maps_open
which has:
priv->mm = proc_mem_open(inode, PTRACE_MODE_READ);

This gives you stable access to mm and all needed permission checks.

Then, in the read routine you can just:
if (!atomic_inc_not_zero(&mm->mm_users))
goto thats_it;

See smaps routines or e.g. environ_read.


Ah! I see what you mean now. Thanks for the clarification!


Rob.