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>

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>
Rik van Riel · Linus Torvalds
1 parent 6e574195b7
Showing 2 changed files with 48 additions and 0 deletions Side-by-side Diff
Documentation/sysrq.txt
drivers/char/sysrq.c
@@ -85,6 +85,8 @@
 '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
@@ -196,6 +196,48 @@
 #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 @@
 	&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 */
...	...	@@ -85,6 +85,8 @@
85	85	'k' - Secure Access Key (SAK) Kills all programs on the current virtual
86	86	console. NOTE: See important comments below in SAK section.
87	87
	88	+'l' - Shows a stack backtrace for all active CPUs.
	89	+
88	90	'm' - Will dump current memory info to your console.
89	91
90	92	'n' - Used to make RT tasks nice-able
...	...	@@ -196,6 +196,48 @@
196	196	#define sysrq_showlocks_op ((struct sysrq_key_op )0)
197	197	#endif
198	198
	199	+#ifdef CONFIG_SMP
	200	+static DEFINE_SPINLOCK(show_lock);
	201	+
	202	+static void showacpu(void *dummy)
	203	+{
	204	+ unsigned long flags;
	205	+
	206	+ /* Idle CPUs have no interesting backtrace. */
	207	+ if (idle_cpu(smp_processor_id()))
	208	+ return;
	209	+
	210	+ spin_lock_irqsave(&show_lock, flags);
	211	+ printk(KERN_INFO "CPU%d:\n", smp_processor_id());
	212	+ show_stack(NULL, NULL);
	213	+ spin_unlock_irqrestore(&show_lock, flags);
	214	+}
	215	+
	216	+static void sysrq_showregs_othercpus(struct work_struct *dummy)
	217	+{
	218	+ smp_call_function(showacpu, NULL, 0, 0);
	219	+}
	220	+
	221	+static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
	222	+
	223	+static void sysrq_handle_showallcpus(int key, struct tty_struct *tty)
	224	+{
	225	+ struct pt_regs *regs = get_irq_regs();
	226	+ if (regs) {
	227	+ printk(KERN_INFO "CPU%d:\n", smp_processor_id());
	228	+ show_regs(regs);
	229	+ }
	230	+ schedule_work(&sysrq_showallcpus);
	231	+}
	232	+
	233	+static struct sysrq_key_op sysrq_showallcpus_op = {
	234	+ .handler = sysrq_handle_showallcpus,
	235	+ .help_msg = "aLlcpus",
	236	+ .action_msg = "Show backtrace of all active CPUs",
	237	+ .enable_mask = SYSRQ_ENABLE_DUMP,
	238	+};
	239	+#endif
	240	+
199	241	static void sysrq_handle_showregs(int key, struct tty_struct *tty)
200	242	{
201	243	struct pt_regs *regs = get_irq_regs();
202	244
...	...	@@ -340,7 +382,11 @@
340	382	&sysrq_kill_op, /* i */
341	383	NULL, /* j */
342	384	&sysrq_SAK_op, /* k */
	385	+#ifdef CONFIG_SMP
	386	+ &sysrq_showallcpus_op, /* l */
	387	+#else
343	388	NULL, /* l */
	389	+#endif
344	390	&sysrq_showmem_op, /* m */
345	391	&sysrq_unrt_op, /* n */
346	392	/* o: This will often be registered as 'Off' at init time */