linux-kernel - [PATCH 2/2] kernel/trace: fix watchdog soft lockup

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Message-Id: <20181128081334.18408-1-anders.roxell@linaro.org>
Date:   Wed, 28 Nov 2018 09:13:34 +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 2/2] 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]'
Each time the function ftrace_replace_code gets called it stays in that
functions loop for 41424 times.
Rework so that function cond_resched() gets called in the
ftrace_replace_code 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/ftrace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 5b4f73e4fd56..3f456921dedf 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2426,6 +2426,10 @@ void __weak ftrace_replace_code(int enable)
 
 	do_for_each_ftrace_rec(pg, rec) {
 
+		/* This loop can take minutes when sanitizers are enabled, so
+		 * lets make sure we allow RCU processing.
+		 */
+		cond_resched();
 		if (rec->flags & FTRACE_FL_DISABLED)
 			continue;
 
-- 
2.19.2