Re: [PATCH 2/5] uprobes: suppress uprobe_munmap() from mmput()

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* 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
>