rts: add missing ccs_mutex guard to internal_dlopen

See added comment for details. Closes #24423.

(cherry picked from commit 20f80b77)

rts/Linker.c

@@ -598,8 +598,27 @@ internal_dlopen(const char *dll_name)
    // (see POSIX also)
 
    ACQUIRE_LOCK(&dl_mutex);
+
+   // When dlopen() loads a profiled dynamic library, it calls the
+   // ctors which will call registerCcsList() to append the defined
+   // CostCentreStacks to CCS_LIST. This execution path starting from
+   // addDLL() was only protected by dl_mutex previously. However,
+   // another thread may be doing other things with the RTS linker
+   // that transitively calls refreshProfilingCCSs() which also
+   // accesses CCS_LIST, and those execution paths are protected by
+   // linker_mutex. So there's a risk of data race that may lead to
+   // segfaults (#24423), and we need to ensure the ctors are also
+   // protected by ccs_mutex.
+#if defined(PROFILING)
+   ACQUIRE_LOCK(&ccs_mutex);
+#endif
+
    hdl = dlopen(dll_name, RTLD_LAZY|RTLD_LOCAL); /* see Note [RTLD_LOCAL] */
 
+#if defined(PROFILING)
+   RELEASE_LOCK(&ccs_mutex);
+#endif
+
    errmsg = NULL;
    if (hdl == NULL) {
       /* dlopen failed; return a ptr to the error msg. */

rts/Profiling.c

@@ -58,7 +58,7 @@ CostCentre      *CC_LIST  = NULL;
 static CostCentreStack *CCS_LIST = NULL;
 
 #if defined(THREADED_RTS)
-static Mutex ccs_mutex;
+Mutex ccs_mutex;
 #endif
 
 /*

rts/Profiling.h

@@ -55,6 +55,10 @@ extern Arena *prof_arena;
 void debugCCS( CostCentreStack *ccs );
 #endif
 
+#if defined(THREADED_RTS)
+extern Mutex ccs_mutex;
+#endif
+
 #endif
 
 #include "EndPrivate.h"