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    SubjectRe: [PATCH v2 1/7] fs/proc/task_mmu.c: don't use task->mm in m_start() and show_*map()
    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@redhat.com>
    > ---
    > 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@linux.intel.com>

    > 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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