On Tue, Aug 05, 2014 at 09:46:44PM +0200, Oleg Nesterov wrote:
> get_gate_vma(priv->task->mm) looks ugly and wrong, task->mm can be
> NULL or it can changed by exec right after mm_access().
>
> And in theory this race is not harmless, the task can exec and then
> later exit and free the new mm_struct. In this case get_task_mm(oldmm)
> can't help, get_gate_vma(task->mm) can read the freed/unmapped memory.
>
> I think that priv->task should simply die and hold_task_mempolicy()
> logic can be simplified. tail_vma logic asks for cleanups too.
>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
> fs/proc/task_mmu.c | 8 +++-----
> 1 files changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index cfa63ee..8a5271e 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -170,7 +170,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
> return mm;
> down_read(&mm->mmap_sem);
>
> - tail_vma = get_gate_vma(priv->task->mm);
> + tail_vma = get_gate_vma(mm);
> priv->tail_vma = tail_vma;
> hold_task_mempolicy(priv);
> /* Start with last addr hint */
> @@ -351,12 +351,11 @@ static int show_map(struct seq_file *m, void *v, int is_pid)
> {
> struct vm_area_struct *vma = v;
> struct proc_maps_private *priv = m->private;
> - struct task_struct *task = priv->task;
>
> show_map_vma(m, vma, is_pid);
>
> if (m->count < m->size) /* vma is copied successfully */
> - m->version = (vma != get_gate_vma(task->mm))
> + m->version = (vma != priv->tail_vma)
> ? vma->vm_start : 0;
Drop excessive parenthesis while you're there? And in the next hunk.
Otherwise:
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> return 0;
> }
> @@ -584,7 +583,6 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> static int show_smap(struct seq_file *m, void *v, int is_pid)
> {
> struct proc_maps_private *priv = m->private;
> - struct task_struct *task = priv->task;
> struct vm_area_struct *vma = v;
> struct mem_size_stats mss;
> struct mm_walk smaps_walk = {
> @@ -639,7 +637,7 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
> show_smap_vma_flags(m, vma);
>
> if (m->count < m->size) /* vma is copied successfully */
> - m->version = (vma != get_gate_vma(task->mm))
> + m->version = (vma != priv->tail_vma)
> ? vma->vm_start : 0;
> return 0;
> }
> --
> 1.5.5.1
>
> --
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--
Kirill A. Shutemov
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