Fix potential deadlock in state_key::Entry::drop #14670
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ziaptos
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Sep 18, 2024
| @@ -152,7 +152,7 @@ where | |||
| let mut locked = self.inner.write(); | |||
| if let Some(map2) = locked.get_mut(key1) { | |||
| if let Some(entry) = map2.get(key2) { | |||
| if entry.upgrade().is_none() { | |||
| if entry.strong_count() == 0 { | |||
| map2.remove(key2); | |||
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Why not move the other conditional inside this if statement, while already here :)
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sure. I tried to think of why I wrote it that way other than one less level of nesting but I can't 🧌
areshand
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Sep 18, 2024
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If before Entry::drop() calls Registry::maybe_remove, the weak ref under the same key1 and key2 is replaced, Entry::drop can be called recursively resulting in a deadlock. The crux is we try to see if the entry has been replaced by trying to upgrading it to a strong ref, and it possible that the upgrade is successful and the result becomes a only ref to the new entry. This tries to fix it by determining the same thing by seeing if Weak::strong_count() is 0 instead of upgrading the weak ref.
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(cherry picked from commit 8eb8b52)
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Description
If before Entry::drop() calls Registry::maybe_remove, the weak ref under the same key1 and key2 is replaced, Entry::drop can be called recursively resulting in a deadlock. The crux is we try to see if the entry has been replaced by trying to upgrading it to a strong ref, and it possible that the upgrade is successful and the result becomes a only ref to the new entry.
This tries to fix it by determining the same thing by seeing if Weak::strong_count() is 0 instead of upgrading the weak ref.
Type of Change
Which Components or Systems Does This Change Impact?
How Has This Been Tested?
eyes of hackers