Re: [PATCH v4 3.0-rc2-tip 7/22] 7: uprobes: mmap and fork hooks.

[Srikar Dronamraju]

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> [2011-07-18 16:31:16]:

> On Mon, 2011-07-18 at 14:50 +0530, Srikar Dronamraju wrote:
> >  *  - Introduce uprobes_list and uprobes_vaddr in vm_area_struct.
> >  *    uprobes_list is a node in the temp list of vmas while
> >  *    registering/unregistering uprobes. uprobes_vaddr caches the vaddr to
> >  *    insert/remove the breakpoint.
> >  *
> >  *  - Introduce srcu to synchronize vma deletion with walking the list of
> >  *    vma in register/unregister_uprobe.
> 
> I don't think you can sell this, that'll make munmap() horridly slow.

Okay, 

How about using a counter and a wq in each vma.
Based on the counter, I can wait in the munmap() and since this is per
vma, this should be faster than srcu.

Counter would be incremented when we do a vma-rmap walk. 
decremented when after insertion/deletion.
read in munmap().

> 
> >  *  - Introduce uprobes_mmap_mutex to synchronize uprobe deletion and
> >  *    mmap_uprobe(). 
> 
> Yes, that'll work I think.

Here another possibility is to have a per uprobe mutex, that way we
would not have to serialize mmap_uprobe. But this optimization can be
done later too.

-- 
Thanks and Regards
Srikar
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