From 5045bcae0fb466a1dbb6af0036e56901fd7aafb7 Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@redhat.com>
Date: Tue, 29 Apr 2008 00:59:21 -0700
Subject: [PATCH] sysrq: add show-backtrace-on-all-cpus function
SysRQ-P is not always useful on SMP systems, since it usually ends up showing
the backtrace of a CPU that is doing just fine, instead of the backtrace of
the CPU that is having problems.
This patch adds SysRQ show-all-cpus(L), which shows the backtrace of every
active CPU in the system. It skips idle CPUs because some SMP systems are
just too large and we already know what the backtrace of the idle task looks
like.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Rik van Riel <riel@redhat.com>
Randy Dunlap <randy.dunlap@oracle.com>
Cc: <lwoodman@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
Documentation/sysrq.txt | 2 ++
drivers/char/sysrq.c | 46 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 48 insertions(+)
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 10c8f6922ef40..5ce0952aa0654 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 1ade193c91281..9e9bad8bdcf4e 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 */
--
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