fs/proc/task_mmu.c: shift "priv->task = NULL" from m_start() to m_stop()

1. There is no reason to reset ->tail_vma in m_start(), if we return
   IS_ERR_OR_NULL() it won't be used.

2. m_start() also clears priv->task to ensure that m_stop() won't use
   the stale pointer if we fail before get_task_struct(). But this is
   ugly and confusing, move this initialization in m_stop().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index b7e31836a005..30aa2dd3e6f5 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -146,17 +146,12 @@ static void *m_start(struct seq_file *m, loff_t *pos)
         struct vm_area_struct *vma, *tail_vma = NULL;
         loff_t l = *pos;
 
-        /* Clear the per syscall fields in priv */
-        priv->task = NULL;
-        priv->tail_vma = NULL;
-
         /*
          * We remember last_addr rather than next_addr to hit with
          * vmacache most of the time. We have zero last_addr at
          * the beginning and also after lseek. We will have -1 last_addr
          * after the end of the vmas.
          */
-
         if (last_addr == -1UL)
                 return NULL;
 
@@ -228,8 +223,10 @@ static void m_stop(struct seq_file *m, void *v)
 
         if (!IS_ERR_OR_NULL(v))
                 vma_stop(priv);
-        if (priv->task)
+        if (priv->task) {
                 put_task_struct(priv->task);
+                priv->task = NULL;
+        }
 }
 
 static int proc_maps_open(struct inode *inode, struct file *file,