Re: RCU: Call touch_nmi_watchdog() while printing stall warnings

Sergey Senozhatsky
2018-01-10T05:34:56Z

Hello,

On (01/09/18 10:47), Tejun Heo wrote:
> When RCU stall warning triggers, it can print out a lot of messages
> while holding spinlocks. If the console device is slow (e.g. an
> actual or IPMI serial console), it may end up triggering NMI hard
> lockup watchdog like the following.
>
> *** CPU printking while holding RCU spinlock
>
> PID: 4149739 TASK: ffff881a46baa880 CPU: 13 COMMAND: "CPUThreadPool8"
> #0 [ffff881fff945e48] crash_nmi_callback at ffffffff8103f7d0
> #1 [ffff881fff945e58] nmi_handle at ffffffff81020653
> #2 [ffff881fff945eb0] default_do_nmi at ffffffff81020c36
> #3 [ffff881fff945ed0] do_nmi at ffffffff81020d32
> #4 [ffff881fff945ef0] end_repeat_nmi at ffffffff81956a7e
> [exception RIP: io_serial_in+21]
> RIP: ffffffff81630e55 RSP: ffff881fff943b88 RFLAGS: 00000002
> RAX: 000000000000ca00 RBX: ffffffff8230e188 RCX: 0000000000000000
> RDX: 00000000000002fd RSI: 0000000000000005 RDI: ffffffff8230e188
> RBP: ffff881fff943bb0 R8: 0000000000000000 R9: ffffffff820cb3c4
> R10: 0000000000000019 R11: 0000000000002000 R12: 00000000000026e1
> R13: 0000000000000020 R14: ffffffff820cd398 R15: 0000000000000035
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0000
> --- <NMI exception stack> ---
> #5 [ffff881fff943b88] io_serial_in at ffffffff81630e55
> #6 [ffff881fff943b90] wait_for_xmitr at ffffffff8163175c
> #7 [ffff881fff943bb8] serial8250_console_putchar at ffffffff816317dc
> #8 [ffff881fff943bd8] uart_console_write at ffffffff8162ac00
> #9 [ffff881fff943c08] serial8250_console_write at ffffffff81634691
> #10 [ffff881fff943c80] univ8250_console_write at ffffffff8162f7c2
> #11 [ffff881fff943c90] console_unlock at ffffffff810dfc55
> #12 [ffff881fff943cf0] vprintk_emit at ffffffff810dffb5
> #13 [ffff881fff943d50] vprintk_default at ffffffff810e01bf
> #14 [ffff881fff943d60] vprintk_func at ffffffff810e1127
> #15 [ffff881fff943d70] printk at ffffffff8119a8a4
> #16 [ffff881fff943dd0] print_cpu_stall_info at ffffffff810eb78c
> #17 [ffff881fff943e88] rcu_check_callbacks at ffffffff810ef133
> #18 [ffff881fff943ee8] update_process_times at ffffffff810f3497
> #19 [ffff881fff943f10] tick_sched_timer at ffffffff81103037
> #20 [ffff881fff943f38] __hrtimer_run_queues at ffffffff810f3f38
> #21 [ffff881fff943f88] hrtimer_interrupt at ffffffff810f442b

Tejun, while we are at it, shall we also touch NMI in show_workqueue_state()?
I suppose that show_pwq() can be quite verbose on some systems, can't it?

for instance: sysrq-t [irq] -> show_workqueue_state()

---

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9960f8842b31..649c00a9af12 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -48,6 +48,7 @@
#include <linux/moduleparam.h>
#include <linux/uaccess.h>
#include <linux/sched/isolation.h>
+#include <linux/nmi.h>

#include "workqueue_internal.h"

@@ -4473,6 +4474,8 @@ void show_workqueue_state(void)
if (pwq->nr_active || !list_empty(&pwq->delayed_works))
show_pwq(pwq);
spin_unlock_irqrestore(&pwq->pool->lock, flags);
+
+ touch_nmi_watchdog();
}
}