Messages in this thread | | | Date | Wed, 30 Nov 2011 11:20:56 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap. |
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> > There's more cases, I forgot the details of how the prio_tree stuff > works, so please consider if its possible to also have: > > __unregister_uprobe() will observe neither old nor new > > This could happen if we first munmap, __unregister_uprobe() will iterate > past where mmap() will insert the new vma, mmap will insert the new vma, > and __unregister_uprobe() will now not observe it. >
- When we iterate thro __unregister_uprobe(), we always walk from the root of the prio tree and not depend on the last found node. So __unregister_uprobe able to iterate thro the rmap without finding the old or the new vma would mean that the exclusive mmap_sem was dropped for atleast a brief period and munmap/mmap are disjoint.
Here munmap_uprobe would have reduced the count followed by the pages being cleared. __unregister_uprobe maintains the status quo. mmap_uprobe would load a new set of pages without any breakpoint, since there are no consumers, and no underlying breakpoints, it also maintains the status quo.
> and > > __unregister_uprobe() will observe both old _and_ new > > This latter could happen by favourably interleaving the prio_tree > iteration with the munmap and mmap operations, so that we first observe > the old vma, do the munmap, do the mmap, and then have the > find_next_vma_info() thing find the new vma.
If __unregister_uprobe() can observe both old _and_ new, then it means mmap has occurred. So its correct that probes are removed from the old and new. The munmap_uprobe of the old vma wouldnt see the breakpoint (via read_opcode) so wont decrement the count. If the munmap_uprobe had seen the breakpoint before unregister_uprobe, then unregister_uprobe cant decrement the count.
-- Thanks and Regards Srikar
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