query_executor: Fixed race between Query.Release() and speculative executions #1684
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@martin-sucha - will you be able to review this change? TIA! |
martin-sucha
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Apr 4, 2023
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Thanks for the pull request! Code looks good to me. Could you please also update AUTHORS and CHANGELOG.md as per https://github.com/gocql/gocql/blob/master/CONTRIBUTING.md#minimum-requirement-checklist ?
…ecutions As described in apache#1315, there is a race condition when there is more than one concurrent execution (by means of speculative execution) and Query.Release() is called after one of them completes. Query.Release() calls Query.reset(), which in turns zeroes the whole Query. Then, after another execution completes, it tries to access metrics, but they are already set to nil by the call to Release(), so a segfault is triggered. The solution is quite simple: a ref counter is introduced into the Query. It is obviously initially set to 1. Every execution fiber (i.e. every execution goroutine) has the refcount atomically incremented before it is started, and decrements the refcount on completion. Query.Release() merely decrements the refcount. Query.reset() is called by whichever goroutine that decrements the refcount to 0.
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Done. |
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@martin-sucha ping |
martin-sucha
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Apr 20, 2023
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Thanks! Merged 🚀 |
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As described in #1315, there is a race condition when there is more than one concurrent execution (by means of speculative execution) and
Query.Release()is called after one of them completes.Query.Release()callsQuery.reset(), which in turns zeroes the wholeQuery. Then, after another execution completes, it tries to access metrics, but they are already set to nil by the call toRelease(), so a segfault is triggered.The solution is quite simple: a ref counter is introduced into the
Query. It is obviously initially set to 1. Every execution fiber (i.e. every execution goroutine) has the refcount atomically incremented before it is started, and decrements the refcount on completion.Query.Release()merely decrements the refcount.Query.reset()is called by whichever goroutine that decrements the refcount to 0.Fixes: #1315