Re: [PATCH 20/24] task_diag: Only add VMAs for thread_group leader

On 07/14, David Ahern wrote:

On 7/14/15 1:47 PM, Oleg Nesterov wrote:

quoted

quoted

  	if (show_flags & TASK_DIAG_SHOW_VMA) {
+		/* if the request is to dump all threads of all processes
+		 * only show VMAs for group leader.
+		 */
+		if (req->dump_strategy == TASK_DIAG_DUMP_ALL_THREAD &&
+		    !thread_group_leader(tsk))
+			goto done;
+

This doesn't look right, group leader can be a zombie with ->mm == NULL,

Seriously?

Yes, the main thread can do sys_exit() / pthread_exit(), although this
is not that common.

I'll find some way to track whether VMAs have been dumped for
a pid.

In case I confused you, the thread_group_leader() check and "goto done"
above are fine, just you can't trust tsk->mm, so

quoted

quoted

  		if (i >= n)
  			err = fill_vma(tsk, skb, cb, &progress, show_flags);

so this probably needs something like find_lock_task_mm().

ok.

Yes, you just need to (try) find a subthread with ->mm != NULL if !tsk->mm,
find_lock_task_mm() can help.

Oleg.