Don't allow simultaneous memory and CPU profiling #3922
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quodlibetor
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Aug 12, 2020
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| // SAFETY: We ensure above that memory profiling is off. | ||
| // Since we hold the mutex, nobody else can be turning it back on in the intervening time. | ||
| let stacks = unsafe { prof_time(Duration::from_secs(10), 99, merge_threads) }.await?; |
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it might be worth adding an explicit drop(_ctl_lock); after this to ensure that we maintain ownership of the lock in the face of refactorings.
quodlibetor
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Aug 12, 2020
benesch
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Aug 12, 2020
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See tikv/pprof-rs#36. Running the pprof CPU profiler at the same time as the jemalloc profiler is apparently UB. It reliably causes deadlocks in Materialize if the jemalloc sampling rate is aggressive enough (e.g. 2^14).
If another user accesses
/profwhile a CPU profile is running, this will have the unfortunate side effect of hanging their page load until the profile is done. We can improve that UX as a follow-up, but it requires a bit of refactoring (it's not as simple as just callingtry_lock) and since it's a purely cosmetic issue, I didn't want it to block this UB safety issue.This change is