runtime: prevent deadlock when profiling signal arrives in stack scan
Precise stack scan needs to unwind the stack. When it is
unwinding the stack, if a profiling signal arrives, which also
does a traceback, it may deadlock in dl_iterate_phdr. Prevent
this deadlock by setting up runtime_in_callers before traceback.
Change-Id: If9b15dd00f1d3f6ce557ea740d9fd6fd3b842879
Reviewed-on: https://go-review.googlesource.com/c/155766
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/libgo/runtime/go-callers.c b/libgo/runtime/go-callers.c
index b16ae0c..78ada7a 100644
--- a/libgo/runtime/go-callers.c
+++ b/libgo/runtime/go-callers.c
@@ -16,7 +16,7 @@
older versions of glibc when a SIGPROF signal arrives while
collecting a backtrace. */
-static uint32 runtime_in_callers;
+uint32 __go_runtime_in_callers;
/* Argument passed to callback function. */
@@ -185,7 +185,7 @@
bool
alreadyInCallers()
{
- return runtime_atomicload(&runtime_in_callers) > 0;
+ return runtime_atomicload(&__go_runtime_in_callers) > 0;
}
/* Gather caller PC's. */
@@ -203,9 +203,9 @@
data.max = m;
data.keep_thunks = keep_thunks;
state = __go_get_backtrace_state ();
- runtime_xadd (&runtime_in_callers, 1);
+ runtime_xadd (&__go_runtime_in_callers, 1);
backtrace_full (state, 0, callback, error_callback, &data);
- runtime_xadd (&runtime_in_callers, -1);
+ runtime_xadd (&__go_runtime_in_callers, -1);
/* For some reason GCC sometimes loses the name of a thunk function
at the top of the stack. If we are skipping thunks, skip that
diff --git a/libgo/runtime/go-unwind.c b/libgo/runtime/go-unwind.c
index 58cb270..158cbd0 100644
--- a/libgo/runtime/go-unwind.c
+++ b/libgo/runtime/go-unwind.c
@@ -792,7 +792,9 @@
scanstackwithmap (void *gcw)
{
_Unwind_Reason_Code code;
+ runtime_xadd (&__go_runtime_in_callers, 1);
code = _Unwind_Backtrace (scanstackwithmap_callback, gcw);
+ runtime_xadd (&__go_runtime_in_callers, -1);
return code == _URC_END_OF_STACK;
}
diff --git a/libgo/runtime/runtime.h b/libgo/runtime/runtime.h
index 21921ec..9f6e251 100644
--- a/libgo/runtime/runtime.h
+++ b/libgo/runtime/runtime.h
@@ -515,3 +515,9 @@
bool probestackmaps(void)
__asm__("runtime.probestackmaps");
+
+// This is set to non-zero when calling backtrace_full. This is used
+// to avoid getting hanging on a recursive lock in dl_iterate_phdr on
+// older versions of glibc when a SIGPROF signal arrives while
+// collecting a backtrace.
+extern uint32 __go_runtime_in_callers;