From 32feddc1fc0a1bd03c44bb4d74d02f53ce39840e Mon Sep 17 00:00:00 2001
From: Stephen Dolan <sdolan@janestreet.com>
Date: Wed, 24 Jun 2020 16:21:30 +0100
Subject: [PATCH] Do not run OCaml code inside signal handlers

---
 otherlibs/systhreads/st_stubs.c | 10 ----------
 runtime/caml/compatibility.h    |  1 -
 runtime/caml/signals.h          |  1 -
 runtime/signals.c               | 15 ---------------
 runtime/signals_byt.c           |  7 +------
 runtime/signals_nat.c           | 11 +++--------
 6 files changed, 4 insertions(+), 41 deletions(-)

diff --git a/otherlibs/systhreads/st_stubs.c b/otherlibs/systhreads/st_stubs.c
index 285466edb..9c96df54f 100644
--- a/otherlibs/systhreads/st_stubs.c
+++ b/otherlibs/systhreads/st_stubs.c
@@ -253,15 +253,6 @@ static void caml_thread_leave_blocking_section(void)
   caml_thread_restore_runtime_state();
 }
 
-static int caml_thread_try_leave_blocking_section(void)
-{
-  /* Disable immediate processing of signals (PR#3659).
-     try_leave_blocking_section always fails, forcing the signal to be
-     recorded and processed at the next leave_blocking_section or
-     polling. */
-  return 0;
-}
-
 /* Hooks for I/O locking */
 
 static void caml_io_mutex_free(struct channel *chan)
@@ -496,7 +487,6 @@ CAMLprim value caml_thread_initialize(value unit)   /* ML */
   caml_scan_roots_hook = caml_thread_scan_roots;
   caml_enter_blocking_section_hook = caml_thread_enter_blocking_section;
   caml_leave_blocking_section_hook = caml_thread_leave_blocking_section;
-  caml_try_leave_blocking_section_hook = caml_thread_try_leave_blocking_section;
 #ifdef NATIVE_CODE
   caml_termination_hook = st_thread_exit;
 #endif
diff --git a/runtime/caml/compatibility.h b/runtime/caml/compatibility.h
index 1ec4df3fe..1c0150e6d 100644
--- a/runtime/caml/compatibility.h
+++ b/runtime/caml/compatibility.h
@@ -264,7 +264,6 @@
 #define something_to_do caml_something_to_do
 #define enter_blocking_section_hook caml_enter_blocking_section_hook
 #define leave_blocking_section_hook caml_leave_blocking_section_hook
-#define try_leave_blocking_section_hook caml_try_leave_blocking_section_hook
 #define enter_blocking_section caml_enter_blocking_section
 #define leave_blocking_section caml_leave_blocking_section
 #define convert_signal_number caml_convert_signal_number
diff --git a/runtime/caml/signals.h b/runtime/caml/signals.h
index 7ec1ad3ba..feaa17eb4 100644
--- a/runtime/caml/signals.h
+++ b/runtime/caml/signals.h
@@ -86,7 +86,6 @@ void caml_setup_stack_overflow_detection(void);
 
 CAMLextern void (*caml_enter_blocking_section_hook)(void);
 CAMLextern void (*caml_leave_blocking_section_hook)(void);
-CAMLextern int (*caml_try_leave_blocking_section_hook)(void);
 #ifdef POSIX_SIGNALS
 CAMLextern int (*caml_sigmask_hook)(int, const sigset_t *, sigset_t *);
 #endif
diff --git a/runtime/signals.c b/runtime/signals.c
index 57bb3fc71..58f37775a 100644
--- a/runtime/signals.c
+++ b/runtime/signals.c
@@ -136,33 +136,18 @@ CAMLno_tsan void caml_record_signal(int signal_number)
 
 /* Management of blocking sections. */
 
-static intnat volatile caml_async_signal_mode = 0;
-
 static void caml_enter_blocking_section_default(void)
 {
-  CAMLassert (caml_async_signal_mode == 0);
-  caml_async_signal_mode = 1;
 }
 
 static void caml_leave_blocking_section_default(void)
 {
-  CAMLassert (caml_async_signal_mode == 1);
-  caml_async_signal_mode = 0;
-}
-
-static int caml_try_leave_blocking_section_default(void)
-{
-  intnat res;
-  Read_and_clear(res, caml_async_signal_mode);
-  return res;
 }
 
 CAMLexport void (*caml_enter_blocking_section_hook)(void) =
    caml_enter_blocking_section_default;
 CAMLexport void (*caml_leave_blocking_section_hook)(void) =
    caml_leave_blocking_section_default;
-CAMLexport int (*caml_try_leave_blocking_section_hook)(void) =
-   caml_try_leave_blocking_section_default;
 
 CAMLno_tsan /* The read of [caml_something_to_do] is not synchronized. */
 CAMLexport void caml_enter_blocking_section(void)
diff --git a/runtime/signals_byt.c b/runtime/signals_byt.c
index 040de03c5..35ee610a3 100644
--- a/runtime/signals_byt.c
+++ b/runtime/signals_byt.c
@@ -46,12 +46,7 @@ static void handle_signal(int signal_number)
   signal(signal_number, handle_signal);
 #endif
   if (signal_number < 0 || signal_number >= NSIG) return;
-  if (caml_try_leave_blocking_section_hook()) {
-    caml_raise_if_exception(caml_execute_signal_exn(signal_number, 1));
-    caml_enter_blocking_section_hook();
-  }else{
-    caml_record_signal(signal_number);
-  }
+  caml_record_signal(signal_number);
   errno = saved_errno;
 }
 
diff --git a/runtime/signals_nat.c b/runtime/signals_nat.c
index 9ee2b2647..6b96a1177 100644
--- a/runtime/signals_nat.c
+++ b/runtime/signals_nat.c
@@ -99,19 +99,14 @@ DECLARE_SIGNAL_HANDLER(handle_signal)
   signal(sig, handle_signal);
 #endif
   if (sig < 0 || sig >= NSIG) return;
-  if (caml_try_leave_blocking_section_hook ()) {
-    caml_raise_if_exception(caml_execute_signal_exn(sig, 1));
-    caml_enter_blocking_section_hook();
-  } else {
-    caml_record_signal(sig);
+  caml_record_signal(sig);
   /* Some ports cache [Caml_state->young_limit] in a register.
      Use the signal context to modify that register too, but only if
      we are inside OCaml code (not inside C code). */
 #if defined(CONTEXT_PC) && defined(CONTEXT_YOUNG_LIMIT)
-    if (caml_find_code_fragment_by_pc((char *) CONTEXT_PC) != NULL)
-      CONTEXT_YOUNG_LIMIT = (context_reg) Caml_state->young_limit;
+  if (caml_find_code_fragment_by_pc((char *) CONTEXT_PC) != NULL)
+    CONTEXT_YOUNG_LIMIT = (context_reg) Caml_state->young_limit;
 #endif
-  }
   errno = saved_errno;
 }