Eliminate cyclic locks in runtime

This change introduces a new deadlock detector for Cosmo's POSIX threads
implementation. Error check mutexes will now track a DAG of nested locks
and report EDEADLK when a deadlock is theoretically possible. These will
occur rarely, but it's important for production hardening your code. You
don't even need to change your mutexes to use the POSIX error check mode
because `cosmocc -mdbg` will enable error checking on mutexes by default
globally. When cycles are found, an error message showing your demangled
symbols describing the strongly connected component are printed and then
the SIGTRAP is raised, which means you'll also get a backtrace if you're
using ShowCrashReports() too. This new error checker is so low-level and
so pure that it's able to verify the relationships of every libc runtime
lock, including those locks upon which the mutex implementation depends.

tool/cosmocc/README.md

@@ -191,15 +191,22 @@ The following supplemental flags are defined by cosmocc:
 - `-mdbg` may be passed when linking programs. It has the same effect as
   `export MODE=dbg` in that it will cause an alternative build of the
   Cosmopolitan Libc runtime to be linked that was built with `-O0 -g`.
-  Under the normal build mode, `--ftrace` output is oftentimes missing
-  important pieces of the puzzle due to inlining. This mode makes it
-  more comprehensible. It's also the only way to make using GDB to
-  troubleshoot issues inside Cosmo Libc work reliably. Please be warned
-  that this flag may enable some heavyweight runtime checks. For
-  example, mmap() will become O(n) rather than O(logn) in an effort to
-  spot data structure corruption. Lastly, the linked Cosmo runtime was
-  compiled with `-fsanitize=undefined` (UBSAN) although you still need
-  to pass that flag too if you want it for your own code.
+  Under the normal build mode, `--ftrace` output generated by your libc
+  is oftentimes missing important details due to inlining. If your build
+  your code with `cosmocc -O0 -mdbg` then `--ftrace` will make much more
+  sense. It's also the only way to make using GDB to troubleshoot issues
+  inside Cosmo Libc work reliably. Please be warned, this flag enables
+  some heavy-hitting runtime checks, such such lock graph validation.
+  The debug Cosmopolitan runtime is able to detect lock cycles globally
+  automatically via your normal usage of `pthread_mutex_t` and then
+  report strongly connected components with C++ symbol demangling. This
+  runtime will absolutely crash your entire process, if it helps you
+  spot a bug. For example, debug cosmo is build with UBSAN so even an
+  undiscovered yet innocent bit shift of a negative number could take
+  you down. So you wouldn't want to use this in prod very often. Please
+  note that passing `-mdbg` doesn't imply `-g -O0 -fsanitize=undefined`
+  which must be passed separately if you want your code to be compiled
+  with the same stuff as libc.
 
 - `-mtiny` may be passed when linking programs. It has the same effect
   as `export MODE=tiny` in that it will cause an alternative build of

tool/net/redbean.c

@@ -6799,6 +6799,8 @@ static int HandleConnection(size_t i) {
     } else {
       switch ((pid = fork())) {
         case 0:
+          lua_repl_wock();
+          lua_repl_lock();
           meltdown = false;
           __isworker = true;
           connectionclose = false;