commit-graph: writing missing parents is a BUG #102
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derrickstolee
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When writing a commit-graph, we write GRAPH_MISSING_PARENT if the parent's object id does not appear in the list of commits to be written into the commit-graph. This was done as the initial design allowed commits to have missing parents, but the final version requires the commit-graph to be closed under reachability. Thus, this GRAPH_MISSING_PARENT value should never be written. However, there are reasons why it could be written! These range from a bug in the reachable-closure code to a memory error causing the binary search into the list of object ids to fail. In either case, we should fail fast and avoid writing the commit-graph file with bad data. Remove the GRAPH_MISSING_PARENT constant in favor of the constant GRAPH_EDGE_LAST_MASK, which has the same value. Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
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/submit |
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Submitted as pull.102.git.gitgitgadget@gmail.com |
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This branch is now known as |
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This patch series was integrated into pu via git@6df4bba. |
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This patch series was integrated into pu via git@e1db812. |
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This patch series was integrated into pu via git@13930be. |
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This patch series was integrated into pu via git@46fb1f8. |
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A user complained that they had the following message in a git command:
In hex, this value is 0x7fffffff, corresponding to the GRAPH_MISSING_PARENT constant. This constant was intended as a way to have the commit-graph store commits with parents that are not also in the commit-graph. During development, however, we chose to require the commit-graph to be closed under reachability. Thus, this value should never be written, and we don't fall back to parsing usual commits when we see the constant.
This actually happened, and the root cause is unknown. This either means the reachable closure logic is broken somewhere, or something caused the binary search to find the parent in our list of commits. This second problem is more likely, as we have seen RAM issues cause corrupted memory before. I'm still investigating the root cause, but for now we can hit a BUG() statement instead of writing bad data.
Thanks,
-Stolee