Fix #13713 and re-fix the runtime events deadlock #13714
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This was referenced Jan 7, 2025
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Can we add the I think the test suite is showing its value, both in this case - and in #13580 - and hope to see label usage pick up on runtime changing PRs 🙏 |
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gasche
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Jan 8, 2025
| /* [user_events_lock] can be acquired during STW, so we must use | ||
| caml_plat_lock_blocking and be careful to avoid triggering any | ||
| STW while holding it */ | ||
| caml_plat_lock_blocking(&user_events_lock); |
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@gadmm I wonder if the following alternative fix would work:
- take the lock
non_blockingfor all the critical sections outside the STW code - in the STW section, do not take
users_events_lock, with a barrier after the user_events-using section to guarantee that no mutators run in parallel
More generally, I think that we can have resources that use non-blocking locks in mutators and are followed by a barrier in STW.
This was referenced Feb 19, 2025
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As noticed by @gasche, after @jmid's report of a deadlock at #13713, the channel finalizer cannot call
caml_plat_lock_non_blocking. This reverts the parts of the change that caused the bug at #13713 and better documents what happens here.Better reasoning about the interaction between
caml_plat_lock_non_blockingandcaml_plat_lock_blockingleads to tighter constraints about how they should be mixed. This shows that the previous patch did not fix the deadlock inside runtime events as thought, so I fix it differently here.