rwlock: avoid Stacked Borrows violation #121630
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Fixes #121626. Changes code recently added in #110211.
It seems like RwLock assumes that code like this is legal:
However, Stacked Borrows makes this illegal. That may be overeager, and indeed Tree Borrows allows this code, but Tree Borrows might also allow too much code, so until we are more sure about the future of the Rust aliasing model we should avoid code like this.
For the RwLock, this means not mixing direct write access to the mutable local variable
node
, with access through (interior mutable) shared references.r? @m-ou-se @joboet