linux-kernel - [PATCH v2 7/7] Test softlockup

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Date:   Thu, 10 Dec 2020 17:00:38 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Laurence Oberman <loberman@...hat.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 7/7] Test softlockup

Trigger busy loop by:
$> cat /proc/version

Stop the busy loop by:
$> cat /proc/consoles

The code also shows the first touch*watchdog() function that hides
softlockup on a "well known" location.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 fs/proc/consoles.c | 5 +++++
 fs/proc/version.c  | 7 +++++++
 2 files changed, 12 insertions(+)

diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
index dfe6ce3505ce..213c0a209a7c 100644
--- a/fs/proc/consoles.c
+++ b/fs/proc/consoles.c
@@ -9,6 +9,8 @@
 #include <linux/seq_file.h>
 #include <linux/tty_driver.h>
 
+extern volatile bool proc_version_wait;
+
 /*
  * This is handler for /proc/consoles
  */
@@ -30,6 +32,9 @@ static int show_console_dev(struct seq_file *m, void *v)
 	unsigned int a;
 	dev_t dev = 0;
 
+	printk("%s: Going to break /proc/version infinite loop\n", __func__);
+	proc_version_wait = false;
+
 	if (con->device) {
 		const struct tty_driver *driver;
 		int index;
diff --git a/fs/proc/version.c b/fs/proc/version.c
index b449f186577f..15ec6a502589 100644
--- a/fs/proc/version.c
+++ b/fs/proc/version.c
@@ -6,8 +6,15 @@
 #include <linux/seq_file.h>
 #include <linux/utsname.h>
 
+volatile bool proc_version_wait;
+
 static int version_proc_show(struct seq_file *m, void *v)
 {
+	printk("%s: Going to wait until stopped\n", __func__);
+	proc_version_wait = true;
+	while (proc_version_wait)
+		cpu_relax();
+
 	seq_printf(m, linux_proc_banner,
 		utsname()->sysname,
 		utsname()->release,
-- 
2.26.2