mirror of https://github.com/citusdata/citus.git
820119c859
In #6314 I refactored the connection cleanup to be simpler to understand and use. However, by doing so I introduced a use-after-free possibility (that valgrind luckily picked up): In the `ShouldShutdownConnection` path of `AfterXactHostConnectionHandling` we free connections without removing the `transactionNode` from the dlist that it might be part of. Before the refactoring this wasn't a problem, because the dlist would be completely reset quickly after in `ResetGlobalVariables` (without reading or writing the dlist entries). The refactoring changed this by moving the `dlist_delete` call to `ResetRemoteTransaction`, which in turn was called in the `!ShouldShutdownConnection` path of `AfterXactHostConnectionHandling`. Thus this `!ShouldShutdownConnection` path would now delete from the `dlist`, but the `ShouldShutdownConnection` path would not. Thus to remove itself the deleting path would sometimes update nodes in the list that were freed right before. There's two ways of fixing this: 1. Call `dlist_delete` from **both** of paths. 2. Call `dlist_delete` from **neither** of the paths. This commit implements the second approach, and #6684 implements the first. We need to choose which approach we prefer. Sidenote: This bug already existed in 11.1, but valgrind didn't catch it back then. My guess is that this happened because #6314 was merged after the initial release branch was cut. Fixes #6638 |
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