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    Subject[PATCH 06/14] uprobes: suppress uprobe_munmap() from mmput()
    uprobe_munmap() does get_user_pages() and it is also called from
    the final mmput()->exit_mmap() path. This slows down exit/mmput()
    for no reason, and I think it is simply dangerous/wrong to try to
    fault-in a page into the dying mm. If nothing else, this happens
    after the last sync_mm_rss(), afaics handle_mm_fault() can change
    the task->rss_stat and make the subsequent check_mm() unhappy.

    Change uprobe_munmap() to check mm->mm_users != 0.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com>
    ---
    kernel/events/uprobes.c | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    index a93b6df..47c4e24 100644
    --- a/kernel/events/uprobes.c
    +++ b/kernel/events/uprobes.c
    @@ -1082,6 +1082,9 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon
    if (!atomic_read(&uprobe_events) || !valid_vma(vma, false))
    return;

    + if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
    + return;
    +
    if (!atomic_read(&vma->vm_mm->uprobes_state.count))
    return;

    --
    1.5.5.1


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