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Date:	Fri, 11 Oct 2013 12:35:53 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Jakub Jelinek <jakub@...hat.com>,
	Richard Henderson <rth@...ddle.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH, -v3] compiler/gcc4: Add quirk for 'asm goto'
 miscompilation bug

On Thu, Oct 10, 2013 at 05:12:19PM +0200, Ingo Molnar wrote:
> 
> * Jakub Jelinek <jakub@...hat.com> wrote:
> 
> > On Thu, Oct 10, 2013 at 07:04:18AM -0700, Richard Henderson wrote:
> > > On 10/10/2013 01:31 AM, Jakub Jelinek wrote:
> > > > Also, for the bitops patch, you probably want an asm_volatile_goto variant.
> > > 
> > > Why?  Asm without output (which asm goto must be) are automatically volatile.
> > 
> > You're right.
> 
> Indeed. Something like the updated version below?
> 
> [ I kept the asm_volatile_goto() naming to make sure the implicit volatile 
>   is visible. ]

Ingo, I applied this patch (as commit c015a7f0b746) on top of
tip/sched/core

        3354781a2184 "sched/numa: Reflow task_numa_group() to avoid a compiler warning"

The below results show that it does fixed the many oops:

/kernel/i386-randconfig-i005-1008/c015a7f0b746d0a7e18b82876bd2b693722479d2

+--------------------------------------------------------------+--------------+--------------+
|                                                              | 3354781a2184 | c015a7f0b746 |
+--------------------------------------------------------------+--------------+--------------+
| WARNING:CPU:PID:at_fs/sysfs/dir.c:sysfs_add_one()            | 9            |              |
| WARNING:CPU:PID:at_lib/kobject.c:kobject_add_internal()      | 9            |              |
| WARNING:CPU:PID:at_drivers/base/driver.c:driver_unregister() | 9            |              |
| WARNING:CPU:PID:at_lib/list_debug.c:__list_add()             | 9            |              |
| kernel_BUG_at_kernel/timer.c                                 | 9            |              |
| invalid_opcode:PREEMPT_SMP                                   | 9            |              |
| Kernel_panic-not_syncing:Fatal_exception_in_interrupt        | 9            |              |
| good_boots                                                   | 0            | 9            |
+--------------------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-r4-1009/c015a7f0b746d0a7e18b82876bd2b693722479d2

+--------------------------------------------------------------+--------------+--------------+
|                                                              | 3354781a2184 | c015a7f0b746 |
+--------------------------------------------------------------+--------------+--------------+
| BUG:kernel_early_hang_without_any_printk_output              | 2            | 3            |
| WARNING:CPU:PID:at_fs/sysfs/dir.c:sysfs_add_one()            | 7            |              |
| WARNING:CPU:PID:at_lib/kobject.c:kobject_add_internal()      | 7            |              |
| WARNING:CPU:PID:at_drivers/base/driver.c:driver_unregister() | 7            |              |
| WARNING:CPU:PID:at_lib/debugobjects.c:debug_print_object()   | 7            |              |
| INFO:trying_to_register_non-static_key                       | 7            |              |
| kernel_BUG_at_kernel/timer.c                                 | 7            |              |
| invalid_opcode:SMP                                           | 7            |              |
| Kernel_panic-not_syncing:Fatal_exception_in_interrupt        | 7            |              |
| good_boots                                                   | 0            | 6            |
+--------------------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-r8-1005/c015a7f0b746d0a7e18b82876bd2b693722479d2

+---------------------------------------------------------------+--------------+--------------+
|                                                               | 3354781a2184 | c015a7f0b746 |
+---------------------------------------------------------------+--------------+--------------+
| BUG:unable_to_handle_kernel_NULL_pointer_dereference_at       | 1            |              |
| Oops:DEBUG_PAGEALLOC                                          | 9            |              |
| kernel_BUG_at_kernel/cred.c                                   | 1            |              |
| invalid_opcode:DEBUG_PAGEALLOC                                | 1            |              |
| Kernel_panic-not_syncing:CRED:put_cred_rcu()sees_with_usage   | 4            |              |
| BUG:unable_to_handle_kernel_paging_request_at                 | 3            |              |
| BUG:unable_to_handle_kernel_NULL_pointer_dereference_at(null) | 5            |              |
| good_boots                                                    | 0            | 9            |
+---------------------------------------------------------------+--------------+--------------+

However it seems that it leads to or increases the chances of early
boot hang:

/kernel/x86_64-randconfig-a1-1009/c015a7f0b746d0a7e18b82876bd2b693722479d2

+-------------------------------------------------+--------------+--------------+
|                                                 | 3354781a2184 | c015a7f0b746 |
+-------------------------------------------------+--------------+--------------+
| good_boots                                      | 9            | 8            |
| BUG:kernel_early_hang_without_any_printk_output | 0            | 1            |
+-------------------------------------------------+--------------+--------------+

/kernel/x86_64-randconfig-a5-1009/c015a7f0b746d0a7e18b82876bd2b693722479d2

+-------------------------------------------------+--------------+--------------+
|                                                 | 3354781a2184 | c015a7f0b746 |
+-------------------------------------------------+--------------+--------------+
| good_boots                                      | 9            | 8            |
| BUG:kernel_early_hang_without_any_printk_output | 0            | 1            |
+-------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-r1-1009/c015a7f0b746d0a7e18b82876bd2b693722479d2

+-------------------------------------------------+--------------+--------------+
|                                                 | 3354781a2184 | c015a7f0b746 |
+-------------------------------------------------+--------------+--------------+
| BUG:kernel_early_hang_without_any_printk_output | 9            | 9            |
+-------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-r7-1009/c015a7f0b746d0a7e18b82876bd2b693722479d2

+--------------------------------------------------+--------------+--------------+
|                                                  | 3354781a2184 | c015a7f0b746 |
+--------------------------------------------------+--------------+--------------+
| BUG:soft_lockup-CPU_stuck_for_s                  | 1            |              |
| INFO:task_blocked_for_more_than_seconds          | 8            | 8            |
| Kernel_panic-not_syncing:hung_task:blocked_tasks | 8            | 8            |
| BUG:kernel_early_hang_without_any_printk_output  | 0            | 1            |
+--------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-r5-1009/c015a7f0b746d0a7e18b82876bd2b693722479d2

+-------------------------------------------------+--------------+--------------+
|                                                 | 3354781a2184 | c015a7f0b746 |
+-------------------------------------------------+--------------+--------------+
| BUG:kernel_early_hang_without_any_printk_output | 9            | 9            |
+-------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-i008-1008/c015a7f0b746d0a7e18b82876bd2b693722479d2

+-------------------------------------------------+--------------+--------------+
|                                                 | 3354781a2184 | c015a7f0b746 |
+-------------------------------------------------+--------------+--------------+
| BUG:kernel_early_hang_without_any_printk_output | 9            | 9            |
+-------------------------------------------------+--------------+--------------+

/kernel/i386-randconfig-i006-1008/c015a7f0b746d0a7e18b82876bd2b693722479d2

+-------------------------------------------------+--------------+--------------+
|                                                 | 3354781a2184 | c015a7f0b746 |
+-------------------------------------------------+--------------+--------------+
| good_boots                                      | 9            | 7            |
| BUG:kernel_early_hang_without_any_printk_output | 0            | 2            |
+-------------------------------------------------+--------------+--------------+

Thanks,
Fengguang
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