gh-148891: prevent crash in HAMT#148928
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KowalskiThomas wants to merge 1 commit intopython:mainfrom
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What is this PR?
Fix for the crash reported and investigated in #148891.
_PyHamt_Assocallocates HAMT nodes, which can trigger GC. A weakref callback or finaliser fired during GC could re-entercontextvar_set, replacingctx->ctx_varsviaPy_SETREFand freeing the old HAMT while_PyHamt_Assocwas still traversing it, causing a use-after-free.The proposed fix is to hold a strong reference to
ctx->ctx_varsduring the_PyHamt_Assoccall, so that a re-entrant free cannot affect the HAMT being traversed.