commit 4856b36cba80a259a78645753520323caca78d0f
Author: Willy Tarreau <w@1wt.eu>
Date:   Wed Aug 21 14:16:02 2019 +0200

    MEDIUM: debug: make the thread dump code show Lua backtraces
    
    When we dump a thread's state (show thread, panic) we don't know if
    anything is happening in Lua, which can be problematic especially when
    calling external functions. With this patch, the thread dump code can
    now detect if we're running in a global Lua task (hlua_process_task),
    or in a TCP or HTTP Lua service (task_run_applet and applet.fct ==
    hlua_applet_tcp_fct or http_applet_http_fct), or a fetch/converter
    from an analyser (s->hlua != NULL). In such situations, it's able to
    append a formatted Lua backtrace of the Lua execution path with
    function names, file names and line numbers.
    
    Note that a shorter alternative could be to call "luaL_where(hlua->T,0)"
    which only prints the current location, but it's not necessarily sufficient
    for complex code.
    
    (cherry picked from commit 78a7cb648ca33823c06430cedc6859ea7e7cd5df)
    [wt: backported to improve troubleshooting when the watchdog fires]
    Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/src/debug.c b/src/debug.c
index 36cc9e71..79bea884 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -26,6 +26,7 @@
 
 #include <proto/cli.h>
 #include <proto/fd.h>
+#include <proto/hlua.h>
 #include <proto/stream_interface.h>
 #include <proto/task.h>
 
@@ -91,6 +92,7 @@ void ha_task_dump(struct buffer *buf, const struct task *task, const char *pfx)
 {
 	const struct stream *s = NULL;
 	const struct appctx __maybe_unused *appctx = NULL;
+	struct hlua __maybe_unused *hlua = NULL;
 
 	if (!task) {
 		chunk_appendf(buf, "0\n");
@@ -117,6 +119,9 @@ void ha_task_dump(struct buffer *buf, const struct task *task, const char *pfx)
 	              task->process == process_stream ? "process_stream" :
 	              task->process == task_run_applet ? "task_run_applet" :
 	              task->process == si_cs_io_cb ? "si_cs_io_cb" :
+#ifdef USE_LUA
+		      task->process == hlua_process_task ? "hlua_process_task" :
+#endif
 		      "?",
 	              task->context);
 
@@ -134,6 +139,30 @@ void ha_task_dump(struct buffer *buf, const struct task *task, const char *pfx)
 
 	if (s)
 		stream_dump(buf, s, pfx, '\n');
+
+#ifdef USE_LUA
+	hlua = NULL;
+	if (s && (hlua = s->hlua)) {
+		chunk_appendf(buf, "%sCurrent executing Lua from a stream analyser -- ", pfx);
+	}
+	else if (task->process == hlua_process_task && (hlua = task->context)) {
+		chunk_appendf(buf, "%sCurrent executing a Lua task -- ", pfx);
+	}
+	else if (task->process == task_run_applet && (appctx = task->context) &&
+		 (appctx->applet->fct == hlua_applet_tcp_fct && (hlua = appctx->ctx.hlua_apptcp.hlua))) {
+		chunk_appendf(buf, "%sCurrent executing a Lua TCP service -- ", pfx);
+	}
+	else if (task->process == task_run_applet && (appctx = task->context) &&
+		 (appctx->applet->fct == hlua_applet_http_fct && (hlua = appctx->ctx.hlua_apphttp.hlua))) {
+		chunk_appendf(buf, "%sCurrent executing a Lua HTTP service -- ", pfx);
+	}
+
+	if (hlua) {
+		luaL_traceback(hlua->T, hlua->T, NULL, 0);
+		if (!append_prefixed_str(buf, lua_tostring(hlua->T, -1), pfx, '\n', 1))
+			b_putchr(buf, '\n');
+	}
+#endif
 }
 
 /* This function dumps all profiling settings. It returns 0 if the output