On 08/09, Srikar Dronamraju wrote:
>
> * Oleg Nesterov <o...@redhat.com> [2012-08-08 19:37:47]:
>
> > Add the new MMF_HAS_UPROBES flag. It is set by install_breakpoint()
> > and it is copied by dup_mmap(), uprobe_pre_sstep_notifier() checks
> > it to avoid the slow path if the task was never probed. Perhaps it
> > makes sense to check it in valid_vma(is_register => false) as well.
> >
> > This needs the new dup_mmap()->uprobe_dup_mmap() hook. We can't use
> > uprobe_reset_state() or put MMF_HAS_UPROBES into MMF_INIT_MASK, we
> > need oldmm->mmap_sem to avoid the race with uprobe_register() or
> > mmap() from another thread.
> >
> > Currently we never clear this bit, it can be false-positive after
> > uprobe_unregister() or uprobe_munmap() or if dup_mmap() hits the
> > probed VM_DONTCOPY vma. But this is fine correctness-wise and has
> > no effect unless the task hits the non-uprobe breakpoint.
> >
>
> In which case, cant we just delete uprobe_munmap() altogether.
>From 0/7:
The next series will teach uprobes to
clear MMF_HAS_UPROBES, but perhaps we should simply remove
uprobe_munmap() instead.
Yes, after this series uprobe_munmap() is nop, but see below.
> > @@ -1034,6 +1045,9 @@ void uprobe_munmap(struct vm_area_struct *vma,
> > unsigned long start, unsigned lon
> > if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
> > return;
> >
> > + if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
> > + return;
> > +
>
> I am not sure whats the purpose of the above test
>
>
>
> > /* TODO: unmapping uprobe(s) will need more work */
>
> and I am unable to think what more we would want to do here.
The next series will add MMF_UPROBE_RECALC, this bits indicates that
MMF_HAS_UPROBES can be false-positive. uprobe_munmap() will roughly do
if (find_node_in_range(start, end))
set_bit(MMF_UPROBE_RECALC);
Once again, I am not sure we really need more complications, we will
discuss this later and decide. If we do not want them, we can kill
uprobe_munmap().
Just in case... uprobe_dup_mmap() is very simple but "sub-optimal".
We can improve this logic if we add uprobe_dup_vma() instead which
does
if (test_bit(MMF_HAS_UPROBES))
return;
if (find_node_in_range(...))
set_bit(MMF_HAS_UPROBES);
But again, it would be better to discuss this later.
Oleg.
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