On Tue, 2011-11-29 at 12:48 +0100, Peter Zijlstra wrote: > There's 2 main cases, > A) vma_adjust() vs unregister_uprobe() and > B) mmap() vs unregister_uprobe(). > > The result of A should be -1 reference in total, since we're removing > the one probe. This might not be correct for A[23], please double check. > The result of B should be 0 since we're removing the > probe and we shouldn't be installing new ones. > > A1) > vma_adjust() > munmap_uprobe() > unregister_uprobe() > mmap_uprobe() > delete_uprobe() > > > munmap will to -1, mmap will do +1, __unregister_uprobe() which is > serialized against vma_adjust() will do -1 on either the old or new vma, > resulting in a grand total of: -1+1-1=-1, OK > > A2) breakpoint is in old, not in new, again two cases: > > A2a) __unregister_uprobe() sees old > > munmap -1, __unregister_uprobe -1, mmap 0: -2 FAIL > > A2b) __unregister_uprobe() sees new > > munmap -1, __unregister_uprobe 0, mmap 0: -1 OK > > A3) breakpoint is in new, not in old, again two cases: > > A3a) __unregister_uprobe() sees old > > munmap 0, __unregister_uprobe 0, mmap: 1: 1 FAIL > > A3b) __unregister_uprobe() seed new > > munmap 0, __unregister_uprobe -1, mmap: 1: 0 FAIL 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. 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. > B1) > unregister_uprobe() > mmap() > mmap_uprobe() > __unregister_uprobe() > delete_uprobe() > > mmap +1, __unregister_uprobe() -1: 0 OK > > B2) > unregister_uprobe() > mmap() > __unregister_uprobe() > mmap_uprobe() > delete_uprobe() > > mmap +1, __unregister_uprobe() 0: +1 FAIL -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href