linux-kernel - [PATCH v2] kernel/trace: fix watchdog soft lockup

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Date:   Fri, 30 Nov 2018 15:56:22 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     rostedt@...dmis.org, mingo@...hat.com
Cc:     akpm@...ux-foundation.org, dvyukov@...gle.com,
        linux-kernel@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v2] kernel/trace: fix watchdog soft lockup

When building a allmodconfig kernel for arm64 and boot that in qemu,
CONFIG_FTRACE_STARTUP_TEST gets enabled and that takes time so the
watchdog expires and prints out a message like this:
'watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [swapper/0:1]'
Depending on what the what test gets called from init_trace_selftests()
it stays minutes in the loop.
Rework so that function cond_resched() gets called in the
init_trace_selftests loop.

Co-developed-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
---
 kernel/trace/trace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5706599ed534..109becbc81ca 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1547,6 +1547,10 @@ static __init int init_trace_selftests(void)
 	pr_info("Running postponed tracer tests:\n");
 
 	list_for_each_entry_safe(p, n, &postponed_selftests, list) {
+		/* This loop can take minutes when sanitizers are enabled, so
+		 * lets make sure we allow RCU processing.
+		 */
+		cond_resched();
 		ret = run_tracer_selftest(p->type);
 		/* If the test fails, then warn and remove from available_tracers */
 		if (ret < 0) {
-- 
2.19.2