[PATCH 08/10] system/cpus: hold off the BQL watchdog under a debugger

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

A debugger stops every thread, so the sequence counter freezes at an
odd value and the watchdog cannot tell that apart from an owner that
never lets go. Attaching gdb to a running guest would report a hang
that is not one.

Skip the report while a tracer is attached, and restart the count so
that a detach gets a full deadline before the watchdog can fire. Any
ptracer sets TracerPid, so strace holds the watchdog off as well.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Cc: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 system/cpus.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/system/cpus.c b/system/cpus.c
index 9e03f303f2..03a07e4824 100644
--- a/system/cpus.c
+++ b/system/cpus.c
@@ -441,6 +441,10 @@ static void *bql_watchdog_fn(void *opaque)
         if (++stuck_polls < BQL_WATCHDOG_POLLS) {
             continue;
         }
+        if (qemu_debugger_attached()) {
+            stuck_polls = 0;
+            continue;
+        }
         if (seq == reported) {
             continue;
         }
-- 
2.53.0