Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap.

[Srikar Dronamraju]

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> [2011-11-23 19:10:12]:

> On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote:
> > +                       ret = install_breakpoint(vma->vm_mm, uprobe);
> > +                       if (ret == -EEXIST) {
> > +                               atomic_inc(&vma->vm_mm->mm_uprobes_count);
> > +                               ret = 0;
> > +                       } 
> 
> Aren't you double counting that probe position here? The one that raced
> you to inserting it will also have incremented that counter, no?
> 

No we arent.
Because register_uprobe can never race with mmap_uprobe and register
before mmap_uprobe registers .(Once we start mmap_region,
register_uprobe waits for the read_lock of mmap_sem.)

And we badly need this for mmap_uprobe case.  Because when we do mremap,
or vma_adjust(), we do a munmap_uprobe() followed by mmap_uprobe() which
would have decremented the count but not removed it. So when we do a
mmap_uprobe, we need to increment the count. 

-- 
Thanks and regards
Srikar

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