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

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Date:   Wed, 5 Apr 2017 15:29:19 +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, Ye Xiaolong wrote:
>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.

Sorry for the late. I applied the patch of on top of the fbc14616f4 ("printk: enable printk offloading") 
and the "reboot-without-waring" issue is gone for 6 times of tests.

testcase/path_params/tbox_group/run: trinity/300s/vm-kbuild-yocto-ia32

fbc14616f483788a  a75384abd8885080d6923d7036  
----------------  --------------------------  
          4:4         -100%            0:6     dmesg.BUG:kernel_reboot-without-warning_in_test_stage

Thanks,
Xiaolong

>
>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
>>