linux-kernel - Re: [printk] fbc14616f4: BUG:kernel_reboot-without-warning_in_test

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Date:   Fri, 31 Mar 2017 14:39:13 +0800
From:   Ye Xiaolong <xiaolong.ye@...el.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Eric Biederman <ebiederm@...ssion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>,
        Len Brown <len.brown@...el.com>, linux-kernel@...r.kernel.org,
        lkp@...org
Subject: Re: [printk]  fbc14616f4:
 BUG:kernel_reboot-without-warning_in_test_stage

On 03/31, Sergey Senozhatsky wrote:
>On (03/31/17 11:35), Sergey Senozhatsky wrote:
>[..]
>> > [   21.009531] VFS: Warning: trinity-c2 using old stat() call. Recompile your binary.
>> > [   21.148898] VFS: Warning: trinity-c0 using old stat() call. Recompile your binary.
>> > [   22.298208] warning: process `trinity-c2' used the deprecated sysctl system call with 
>> > 
>> > Elapsed time: 310
>> > BUG: kernel reboot-without-warning in test stage
>> 
>> so as far as I understand, this is the "missing kernel messages"
>> type of bug report. a worst case scenario.
>
>panic() should have called console_flush_on_panic(), which sould have
>flushed the messages regardless the printk_kthread state. so it probably
>was not panic() that rebooted the kernel. (probably).
>
>kernel_restart() and kernel_halt() have pr_emerg() messages, printk switches
>to printk_emergency mode the first time it sees EMERG level message. (may be
>we switch to late).
>
>on the other hand, there is a emergency_restart(), where we don't switch
>to printk_emergency mode and don't flush the existing kernel messages.
>there is a bunch of places that call emergency_restart(), including sysrq.
>
>may I ask you, how do you usually restart the vm after the test?
>`echo X > /proc/sysrq-trigger'?

Yes.

>
>does this patch make it any better?

I am trying it and will post the result once I get it.

Thanks,
Xiaolong
>
>---
> drivers/tty/sysrq.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
>diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
>index 817dfb69914d..069f5540be36 100644
>--- a/drivers/tty/sysrq.c
>+++ b/drivers/tty/sysrq.c
>@@ -240,7 +240,6 @@ static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
> 
> static void sysrq_handle_showallcpus(int key)
> {
>-	printk_emergency_begin();
> 	/*
> 	 * Fall back to the workqueue based printing if the
> 	 * backtrace printing did not succeed or the
>@@ -255,7 +254,6 @@ static void sysrq_handle_showallcpus(int key)
> 		}
> 		schedule_work(&sysrq_showallcpus);
> 	}
>-	printk_emergency_end();
> }
> 
> static struct sysrq_key_op sysrq_showallcpus_op = {
>@@ -282,10 +280,8 @@ static struct sysrq_key_op sysrq_showregs_op = {
> 
> static void sysrq_handle_showstate(int key)
> {
>-	printk_emergency_begin();
> 	show_state();
> 	show_workqueue_state();
>-	printk_emergency_end();
> }
> static struct sysrq_key_op sysrq_showstate_op = {
> 	.handler	= sysrq_handle_showstate,
>@@ -296,9 +292,7 @@ static struct sysrq_key_op sysrq_showstate_op = {
> 
> static void sysrq_handle_showstate_blocked(int key)
> {
>-	printk_emergency_begin();
> 	show_state_filter(TASK_UNINTERRUPTIBLE);
>-	printk_emergency_end();
> }
> static struct sysrq_key_op sysrq_showstate_blocked_op = {
> 	.handler	= sysrq_handle_showstate_blocked,
>@@ -537,6 +531,7 @@ void __handle_sysrq(int key, bool check_mask)
> 	int orig_log_level;
> 	int i;
> 
>+	printk_emergency_begin();
> 	rcu_sysrq_start();
> 	rcu_read_lock();
> 	/*
>@@ -582,6 +577,7 @@ void __handle_sysrq(int key, bool check_mask)
> 	}
> 	rcu_read_unlock();
> 	rcu_sysrq_end();
>+	printk_emergency_end();
> }
> 
> void handle_sysrq(int key)
>-- 
>2.12.2
>