[issue764] hg strip can create a cross between changelog revs and manifest linkrevs, leading to eventual corruption

[Richard Lowe]

New submission from Richard Lowe <richlowe at richlowe.net>:

it's possible for strip to create a situation where a changelog rev, and a
manifest link rev cross:

cl       man
10 -> 11
11 -> 10

Which, if strip is then used again, will cause a dangling linkrev in the
manifest, and thus repo corruption.

A snippet from #mercurial, about this issue is probably the better explanation:
<cmason> mpm, ok I finally get it
<cmason> (how the crossover happens)
<cmason> we start with a valid repo that looks like this:
<cmason> changeset 5 -> manifest 2
<cmason> changeset 3 -> manifest 3
<cmason> manifest 2 has a linkrev -> changeset 2
<cmason> changeset 2 only has one child, changeset 4.  So, stripping 
                changeset 2 means we have to bundle off changesets 3 and 5 and 
                unbundle them later
<cmason> when we unbundle, we go in changeset order.  changeset 3 first 
                and then changeset 5
<cmason> but, the manifests stored in the bundle were pulled right out 
                of the manifest revlog.  this produces the cross

a script to reproduce this is attached.

----------
files: test-strip.sh
messages: 4071
nosy: richlowe
priority: urgent
status: unread
title: hg strip can create a cross between changelog revs and manifest linkrevs, leading to eventual corruption

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Mercurial issue tracker <mercurial-bugs at selenic.com>
<http://www.selenic.com/mercurial/bts/issue764>
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