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SubjectRe: [PATCH 2/5] uprobes: suppress uprobe_munmap() from mmput()
* Oleg Nesterov <oleg@redhat.com> [2012-07-08 22:30:03]:

> 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@linux.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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