Avoid double-free in regex timeout after stack_double #12030
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jhawthorn
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As of 1057485, it's possible to crash on a double free due to `stk_alloc` AKA `msa->stack_p` being freed twice, once at the end of match_at and a second time in `FREE_MATCH_ARG` in the parent caller. Fixes [Bug #20886]
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https://bugs.ruby-lang.org/issues/20886
As of #11238, certain regex we end up freeing
stk_allocAKAmsa->stack_ptwice, once in FREE_MATCH_ARG and once in the code here. This is very similar to a problem which was previously fixed by 6f6a2d2.This one is a bit hard to reproduce. I'm still searching if there is a more reliable way to reproduce (either too short or too long a timeout and it doesn't seem to occur). I'll continue that tomorrow and then file a bug in the tracker for backport.
cc @composerinteralia @peterzhu2118