misc: Add a lockup driver to get the CPUs wedged

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

1 files changed, 102 insertions, 0 deletions

diff --git a/drivers/misc/lockup.c b/drivers/misc/lockup.c
new file mode 100644
index 000000000000..674a1a228a8a
--- /dev/null
+++ b/drivers/misc/lockup.c
@@ -0,0 +1,102 @@
+/*
+ * lockup.c
+ *
+ * Deliberately do "stupid" things to see if we can debug them
+ * properly.
+ *
+ * The sole purpose of this module is to help with debugging of system
+ * debug tools.
+ *
+ * Copyright (C) 2014 Linaro Limited
+ *                    Daniel Thompson <daniel.thompson@linaro.org>
+ */
+
+#include <linux/module.h>
+#include <linux/debugfs.h>
+#include <linux/debug_locks.h>
+
+static DEFINE_SPINLOCK(lockup_lock);
+
+static int lockup_do_action_on_cpu(int cpu, long (*action)(void *))
+{
+	if (cpu == -1)
+		(void) action(NULL);
+
+	if (cpu < 0 || cpu > num_possible_cpus())
+		return -EINVAL;
+
+	/* work_on_cpu() ends up performing an uninterruptible
+	 * wait-for-completion. This means we'll lose the prompt
+	 * regardless of the CPU we send the work to.
+	 */
+	work_on_cpu(cpu, action, NULL);
+
+	return 0;
+}
+
+#define DEFINE_LOCKUP_ATTRIBUTE(__fops, __action)                              \
+static int __fops ## _set(void *data, u64 val)                                 \
+{                                                                              \
+	lockup_do_action_on_cpu(val, __action);                                \
+	return 0;                                                              \
+}                                                                              \
+DEFINE_SIMPLE_ATTRIBUTE(__fops, NULL, __fops ## _set, "%llu\n")
+
+
+static long do_lockup_spin_lock(void *info)
+{
+	pr_warn("lockup[%u]: About to wedge in spin_lock\n", get_cpu());
+	spin_lock(&lockup_lock);
+	debug_locks_off();
+	spin_lock(&lockup_lock);
+	spin_unlock(&lockup_lock);
+	spin_unlock(&lockup_lock);
+	return 0;
+}
+DEFINE_LOCKUP_ATTRIBUTE(lockup_spin_lock_fops, do_lockup_spin_lock);
+
+static long do_lockup_spin_lock_irqsave(void *info)
+{
+	unsigned long flags1, flags2;
+
+	pr_warn("lockup[%u]: About to wedge in spin_lock_irqsave\n", get_cpu());
+	spin_lock_irqsave(&lockup_lock, flags1);
+	debug_locks_off();
+	spin_lock_irqsave(&lockup_lock, flags2);
+	spin_unlock_irqrestore(&lockup_lock, flags2);
+	spin_unlock_irqrestore(&lockup_lock, flags1);
+	return 0;
+}
+DEFINE_LOCKUP_ATTRIBUTE(lockup_spin_lock_irqsave_fops,
+			do_lockup_spin_lock_irqsave);
+
+static int __init lockup_init(void)
+{
+#define E(x) { #x, &lockup_##x##_fops }
+	const struct {
+		const char *name;
+		const struct file_operations *fops;
+	} fops_table[] = {
+		E(spin_lock),
+		E(spin_lock_irqsave)
+	};
+#undef E
+
+	struct dentry *dir;
+	unsigned int i;
+
+	dir = debugfs_create_dir("lockup", NULL);
+	if (dir)
+		for (i = 0; i < ARRAY_SIZE(fops_table); i++)
+			(void)debugfs_create_file(fops_table[i].name,
+						  S_IRUGO | S_IWUSR, dir, NULL,
+						  fops_table[i].fops);
+
+	pr_info("lockup: create 'lockup' attribute\n");
+	return 0;
+}
+
+module_init(lockup_init);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Daniel Thompson");