Messages in this thread | | | Date | Thu, 9 Aug 2012 16:17:40 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 5/7] uprobes: introduce MMF_HAS_UPROBES |
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On 08/09, Srikar Dronamraju wrote: > > * Oleg Nesterov <oleg@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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