Data race in concurrent uses of `Re.exec` on one pre-compiled Re.re

[kit-ty-kate]

Using TSan with OCaml 5.2 on a code that use re.1.11.0, I'm getting the following error:

WARNING: ThreadSanitizer: data race (pid=76587)
  Read of size 8 at 0xffff60737008 by thread T16 (mutexes: write M0):
    #0 camlRe__Core.loop_1012 lib/core.ml:166 (opamMain.exe+0xbe42e4) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #1 camlRe__Core.match_str_1142 lib/core.ml:304 (opamMain.exe+0xbe57ec) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #2 camlRe__Core.exec_2101 lib/core.ml:941 (opamMain.exe+0xbec9f8) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #3 camlOpamUrl.fun_1957 src/core/opamUrl.ml:70 (opamMain.exe+0xb83a88) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    ...

  Previous write of size 8 at 0xffff60737008 by thread T1 (mutexes: write M1):
    #0 caml_modify runtime/memory.c:220 (opamMain.exe+0xe287fc) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #1 camlRe__Core.validate_991 lib/core.ml:162 (opamMain.exe+0xbe4108) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #2 camlRe__Core.loop_1012 lib/core.ml:175 (opamMain.exe+0xbe4454) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #3 camlRe__Core.match_str_1142 lib/core.ml:304 (opamMain.exe+0xbe57ec) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #4 camlRe__Core.exec_2101 lib/core.ml:941 (opamMain.exe+0xbec9f8) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    #5 camlOpamUrl.fun_1957 src/core/opamUrl.ml:70 (opamMain.exe+0xb83a88) (BuildId: ae1ab72786b3638d51b987620a76af5acea9e7b6)
    ...

The code in opam that uses Re is the following: https://github.com/ocaml/opam/blob/391333d35bcdc8b55df709b876b8bafcf75f3452/src/core/opamUrl.ml#L46-L74 and can be summarized into:

let f =
  let re = Re.compile ... in
  fun str -> Re.exec re str

which then trigger the data race on this piece of mutable state: https://github.com/ocaml/ocaml-re/blob/2dd38515c76c40299596d39f18d9b9a20f00d788/lib/core.ml#L162 https://github.com/ocaml/ocaml-re/blob/2dd38515c76c40299596d39f18d9b9a20f00d788/lib/core.ml#L166