[PATCH] sysrq: do not omit current cpu when showing backtrace of all active CPUs

[Changbin Du]

The backtrace of current CPU also should be printed as it is active. This
change add stack trace for current CPU and print a hint for idle CPU for
the generic workqueue based printing. (x86 already does this)

Now it looks like below:
[  279.401567] sysrq: Show backtrace of all active CPUs
[  279.407234] sysrq: CPU5:
[  279.407505] Call Trace:
[  279.408789] [<ffffffff8000606c>] dump_backtrace+0x2c/0x3a
[  279.411698] [<ffffffff800060ac>] show_stack+0x32/0x3e
[  279.411809] [<ffffffff80542258>] sysrq_handle_showallcpus+0x4c/0xc6
[  279.411929] [<ffffffff80542f16>] __handle_sysrq+0x106/0x26c
[  279.412034] [<ffffffff805436a8>] write_sysrq_trigger+0x64/0x74
[  279.412139] [<ffffffff8029cd48>] proc_reg_write+0x8e/0xe2
[  279.412252] [<ffffffff8021a8f8>] vfs_write+0x90/0x2be
[  279.412362] [<ffffffff8021acd2>] ksys_write+0xa6/0xce
[  279.412467] [<ffffffff8021ad24>] sys_write+0x2a/0x38
[  279.412689] [<ffffffff80003ff8>] ret_from_syscall+0x0/0x2
[  279.417173] sysrq: CPU6: backtrace skipped as idling
[  279.417185] sysrq: CPU4: backtrace skipped as idling
[  279.417187] sysrq: CPU0: backtrace skipped as idling
[  279.417181] sysrq: CPU7: backtrace skipped as idling
[  279.417190] sysrq: CPU1: backtrace skipped as idling
[  279.417193] sysrq: CPU3: backtrace skipped as idling
[  279.417219] sysrq: CPU2:
[  279.419179] Call Trace:
[  279.419440] [<ffffffff8000606c>] dump_backtrace+0x2c/0x3a
[  279.419782] [<ffffffff800060ac>] show_stack+0x32/0x3e
[  279.420015] [<ffffffff80542b30>] showacpu+0x5c/0x96
[  279.420317] [<ffffffff800ba71c>] flush_smp_call_function_queue+0xd6/0x218
[  279.420569] [<ffffffff800bb438>] generic_smp_call_function_single_interrupt+0x14/0x1c
[  279.420798] [<ffffffff800079ae>] handle_IPI+0xaa/0x13a
[  279.421024] [<ffffffff804dcb92>] riscv_intc_irq+0x56/0x70
[  279.421274] [<ffffffff80a05b70>] generic_handle_arch_irq+0x6a/0xfa
[  279.421518] [<ffffffff80004006>] ret_from_exception+0x0/0x10
[  279.421750] [<ffffffff80096492>] rcu_idle_enter+0x16/0x1e

Signed-off-by: Changbin Du <changbin.du at gmail.com>
---
 drivers/tty/sysrq.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index bbfd004449b5..34cfdda4aff5 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -232,8 +232,10 @@ static void showacpu(void *dummy)
 	unsigned long flags;
 
 	/* Idle CPUs have no interesting backtrace. */
-	if (idle_cpu(smp_processor_id()))
+	if (idle_cpu(smp_processor_id())) {
+		pr_info("CPU%d: backtrace skipped as idling\n", smp_processor_id());
 		return;
+	}
 
 	raw_spin_lock_irqsave(&show_lock, flags);
 	pr_info("CPU%d:\n", smp_processor_id());
@@ -260,10 +262,13 @@ static void sysrq_handle_showallcpus(int key)
 
 		if (in_hardirq())
 			regs = get_irq_regs();
-		if (regs) {
-			pr_info("CPU%d:\n", smp_processor_id());
+
+		pr_info("CPU%d:\n", smp_processor_id());
+		if (regs)
 			show_regs(regs);
-		}
+		else
+			show_stack(NULL, NULL, KERN_INFO);
+
 		schedule_work(&sysrq_showallcpus);
 	}
 }
-- 
2.32.0