2 files changed, 48 insertions, 0 deletions

diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 10c8f6922ef4..5ce0952aa065 100644
--- a/Documentation/sysrq.txt
+++ b/Documentation/sysrq.txt
@@ -85,6 +85,8 @@ On all -  write a character to /proc/sysrq-trigger.  e.g.:
 'k'     - Secure Access Key (SAK) Kills all programs on the current virtual
           console. NOTE: See important comments below in SAK section.
 
+'l'     - Shows a stack backtrace for all active CPUs.
+
 'm'     - Will dump current memory info to your console.
 
 'n'     - Used to make RT tasks nice-able
diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 1ade193c9128..9e9bad8bdcf4 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -196,6 +196,48 @@ static struct sysrq_key_op sysrq_showlocks_op = {
 #define sysrq_showlocks_op (*(struct sysrq_key_op *)0)
 #endif
 
+#ifdef CONFIG_SMP
+static DEFINE_SPINLOCK(show_lock);
+
+static void showacpu(void *dummy)
+{
+        unsigned long flags;
+
+        /* Idle CPUs have no interesting backtrace. */
+        if (idle_cpu(smp_processor_id()))
+                return;
+
+        spin_lock_irqsave(&show_lock, flags);
+        printk(KERN_INFO "CPU%d:\n", smp_processor_id());
+        show_stack(NULL, NULL);
+        spin_unlock_irqrestore(&show_lock, flags);
+}
+
+static void sysrq_showregs_othercpus(struct work_struct *dummy)
+{
+        smp_call_function(showacpu, NULL, 0, 0);
+}
+
+static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
+
+static void sysrq_handle_showallcpus(int key, struct tty_struct *tty)
+{
+        struct pt_regs *regs = get_irq_regs();
+        if (regs) {
+                printk(KERN_INFO "CPU%d:\n", smp_processor_id());
+                show_regs(regs);
+        }
+        schedule_work(&sysrq_showallcpus);
+}
+
+static struct sysrq_key_op sysrq_showallcpus_op = {
+        .handler        = sysrq_handle_showallcpus,
+        .help_msg       = "aLlcpus",
+        .action_msg     = "Show backtrace of all active CPUs",
+        .enable_mask    = SYSRQ_ENABLE_DUMP,
+};
+#endif
+
 static void sysrq_handle_showregs(int key, struct tty_struct *tty)
 {
         struct pt_regs *regs = get_irq_regs();
@@ -340,7 +382,11 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
         &sysrq_kill_op,                 /* i */
         NULL,                           /* j */
         &sysrq_SAK_op,                  /* k */
+#ifdef CONFIG_SMP
+        &sysrq_showallcpus_op,          /* l */
+#else
         NULL,                           /* l */
+#endif
         &sysrq_showmem_op,              /* m */
         &sysrq_unrt_op,                 /* n */
         /* o: This will often be registered as 'Off' at init time */