[PATCH] sysrq: add a show-stacktrace-on-all-cpus command

[Avi Kivity <avi@qumranet.com>]

If a cpu is spinning in the kernel but still responding to interrupts,
pressing sysrq-y will show you where it's spinning.

Signed-off-by: Avi Kivity <avi@qumranet.com>

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 39cc318..1dda709 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -45,6 +45,8 @@ int __read_mostly __sysrq_enabled = 1;
 
 static int __read_mostly sysrq_always_enabled;
 
+static spinlock_t show_stack_lock = SPIN_LOCK_UNLOCKED;
+
 int sysrq_on(void)
 {
 	return __sysrq_enabled || sysrq_always_enabled;
@@ -309,6 +311,26 @@ static struct sysrq_key_op sysrq_unrt_op = {
 	.enable_mask	= SYSRQ_ENABLE_RTNICE,
 };
 
+static void show_cpu_stack(void *garbage)
+{
+	spin_lock(&show_stack_lock);
+	printk("CPU%d stacktrace:\n", raw_smp_processor_id());
+	dump_stack();
+	sysrq_handle_showregs(0, NULL);
+	spin_unlock(&show_stack_lock);
+}
+
+static void sysrq_show_stacks(int key, struct tty_struct *tty)
+{
+	on_each_cpu(show_cpu_stack, NULL, 0, 1);
+}
+
+static struct sysrq_key_op sysrq_show_stacks_op = {
+	.handler	= sysrq_show_stacks,
+	.help_msg	= "stacktraces-on-all-cpus(Y)",
+	.action_msg	= "Stack traces on all cpus",
+};
+
 /* Key Operations table and lock */
 static DEFINE_SPINLOCK(sysrq_key_table_lock);
 
@@ -356,7 +378,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
 	&sysrq_showstate_blocked_op,	/* w */
 	/* x: May be registered on ppc/powerpc for xmon */
 	NULL,				/* x */
-	NULL,				/* y */
+	&sysrq_show_stacks_op,		/* y */
 	NULL				/* z */
 };