beacon_node, consensus: fix possible deadlocks when comparing with itself#1241
beacon_node, consensus: fix possible deadlocks when comparing with itself#1241paulhauner merged 1 commit intosigp:masterfrom
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Great find, thanks @BurtonQin! |
| /// Compare two operation pools. | ||
| impl<T: EthSpec + Default> PartialEq for OperationPool<T> { | ||
| fn eq(&self, other: &Self) -> bool { | ||
| if self as *const _ == other as *const _ { |
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I'm wondering if we should be using std::ptr::eq as per Why can comparing two seemingly equal pointers with == return false?
@michaelsproul do you have thoughts here? I'm not particularly well versed here.
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Yeah ptr::eq looks like it might be cleaner. Given this PartialEq impl is only used in tests, I'd be interested in potentially removing it in future.
Other alternatives that I could think of are:
- Make the RHS of the
PartialEq&mut Self, so that self comparisons are statically prevented (although that would be a bit gross to use) - Use a timeout on the RwLock, knowing that it's only used for tests
paulhauner
added
bug
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CI failed with a weird permissions error on MacOS. Rerunning to see if it happens again. |
I saw this somewhere else as well, so perhaps not just a one-off. I have attempted a fix in #1246 |
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Proposed Changes
This PR fixes possible deadlock bugs in beacon_node/operation_pool and consensus/proto_array_fork_choice.
Both are in fn
eq(&self, other: &Self).When
selfandotherrefers to the same obj, (i.e. comparing with itself),the first Read lock is not released before calling the second Read lock.
The lock is a
parking_lot::RwLock.According to the doc of
parking_lot::RwLock:“readers trying to acquire the lock will block even if the lock is unlocked when there are writers waiting to acquire the lock.”
“attempts to recursively acquire a read lock within a single thread may result in a deadlock.”
Therefore, a deadlock may happen when a write lock interleaves the two read locks.
This PR compares the ptr addresses first to avoid comparing with itself.