Comment about proc-dont-lock-task_structs-indefinitely.patch

["Prasanna Meda" <mlp@google.com>]

Hi,

   In reply to http://marc.theaimsgroup.com/?l=linux-kernel&m=114119848908725&q=raw
I was not following and  just noticed it.  The bug is introduced in the patch
http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.16/2.6.16-mm1/broken-out/proc-dont-lock-task_structs-indefinitely.patch

The task decrement problem is fixed, but I think we have two more
problems in the following patch segment.

The priv->tail_vma should not be set NULL; In old code, the local
variable tail vma was overloaded for two more purposes as return value
and also in version calculation, in addition to beging initialised
from  gate vma. It we set the priv->tail_vma as NULL as the following
patch does, and if we seek back, we will not be able to see the gate
vma anymore from m_next.

@@ -337,35 +349,37 @@ static void *m_start(struct seq_file *m,
 	}

 	if (l != mm->map_count)
-		tail_vma = NULL; /* After gate vma */
+		priv->tail_vma = NULL; /* After gate vma */

 out:
  	if (vma)
  		return vma;

  	/* End of vmas has been reached */
-	m->version = (tail_vma != NULL)? 0: -1UL;
+	m->version = (priv->tail_vma != NULL)? 0: -1UL;
 	up_read(&mm->mmap_sem);
  	mmput(mm);
-	return tail_vma;
+	return priv->tail_vma;


Thanks,
Prasanna.
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