Re: [PATCH v7 3.2-rc2 3/30] uprobes: register/unregister probes.

[Srikar Dronamraju]

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> [2011-11-28 16:29:54]:

> On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote:
> > +static void __unregister_uprobe(struct inode *inode, loff_t offset,
> > +                                               struct uprobe *uprobe)
> > +{
> > +       struct list_head try_list;
> > +       struct address_space *mapping;
> > +       struct vma_info *vi, *tmpvi;
> > +       struct vm_area_struct *vma;
> > +       struct mm_struct *mm;
> > +       loff_t vaddr;
> > +
> > +       mapping = inode->i_mapping;
> > +       INIT_LIST_HEAD(&try_list);
> > +       while ((vi = find_next_vma_info(&try_list, offset,
> > +                                               mapping, false)) != NULL) {
> > +               if (IS_ERR(vi))
> > +                       break;
> 
> So what kind of half-assed state are we left in if we try an unregister
> under memory pressure and how do we deal with that?
> 

Agree, Even I had this concern and wanted to see if there are ways to
deal with this.

- One approach would be pass extra GFG flags while we do allocations
  atleast in the unregister_uprobe.

Drawback of this approach: if the system is already under memory
pressure we shouldnt exert more pressure by asking it to repeat.

- The other approach would be to cache these temporary objects while we
  insert probes. i.e keep these metadata around.

I am sure you wouldnt want to add additional metadata.

- Third approach would be to have a completion/worker routine kick in if
  unregister_uprobe fails due to memory allocations.

This looks better than the rest.

Do you have any other approaches that we could try?

-- 
thanks and regards
Srikar

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