Hugh Dickins wrote:
> Better late than never, I've at last reviewed the madvise vma merging
> going into 2.6.13. Remove a pointless check and fix two little bugs -
> a simple test (with /proc/<pid>/maps hacked to show ReadHints) showed
> both mismerges in practice: though being madvise, neither was disastrous.
>
> 1. Correct placement of the success label in madvise_behavior: as in
> mprotect_fixup and mlock_fixup, it is necessary to update vm_flags
> when vma_merge succeeds (to handle the exceptional Case 8 noted in
> the comments above vma_merge itself).
>
> 2. Correct initial value of prev when starting part way into a vma: as
> in sys_mprotect and do_mlock, it needs to be set to vma in this case
> (vma_merge handles only that minimum of cases shown in its comments).
>
> 3. If find_vma_prev sets prev, then the vma it returns is prev->vm_next,
> so it's pointless to make that same assignment again in sys_madvise.
Acknowledge corrections 1 and 3 readily. Treated vma_merge
as block box that can handle all cases. Motivation for pointless
case 3 is to skip holes and did not notice that has been covered. Thanks for
corrections.
> (vma_merge handles only that minimum of cases shown in its comments).
>
Correction 2 is tricky. Sometimes it merges similar to case 3,
misses a needed split, where after the fix we can get case 4
merge. If that is what you are saying, we are in agreement. Otherwise,
can you explain the real problem?
Thanks,
Prasanna.
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