Re: [PATCH v2] generic-ipi: Initialize call_single_queue before enabling interrupt

[Takao Indoh <indou.takao@jp.fujitsu.com>]

On Wed, 06 Apr 2011 18:47:36 -0400, Takao Indoh wrote:

>On Wed, 6 Apr 2011 16:47:42 -0400, Vivek Goyal wrote:
>
>>On Tue, Mar 29, 2011 at 12:35:04PM -0400, Takao Indoh wrote:
>>> Hi all,
>>> 
>>> This patch renames init_call_single_data() to call_function_init() and
>>> calls it in start_kernel() so that call_single_queue can be initialized
>>> before enabling interrupt.
>>> 
>>> There is a problem that kdump(2nd kernel) sometimes hangs up due to
>>> pending IPI from 1st kernel. Kernel panic occurs because IPI comes
>>> before call_single_queue is initialized. The details are as follows.
>>> (1) 2nd kernel boot up
>>> (2) A pending IPI from 1st kernel comes when irqs are first enabled
>>>     in start_kernel().
>>> (3) Kernel tries to handle the interrupt, but call_single_queue is not
>>>     initialized yet at this point. As a result, in the
>>>     generic_smp_call_function_single_interrupt(), NULL pointer
>>>     dereference occurs when list_replace_init() tries to access
>>>     &q->list.next.
>>> Therefore this patch changes the name of init_call_single_data() to
>>> call_function_init() and calls it before local_irq_enable() in
>>> start_kernel().
>>> 
>>> v2:
>>> - Rename init_call_single_data() to call_function_init() and calls it in
>>>   start_kernel()
>>> - Change insert position in start_kernel().
>>> - Adjust for CONFIG_SMP/CONFIG_USE_GENERIC_SMP_HELPERS options
>>> - Rebased to Linus's latest tree
>>> 
>>> v1:
>>> https://lkml.org/lkml/2011/3/25/317
>>> - Divide init_call_single_data() into two functions,
>>>    o init_call_single_data: initialize call_single_queue
>>>    o init_hotplug_cfd: initialize hotplug_cfd_notifier
>>>   And call init_call_single_data before local_irq_enable() in
>>>   start_kernel().
>>> 
>>> v0:
>>> https://lkml.org/lkml/2011/3/23/417
>>> - In generic_smp_call_function_single_interrupt(), check if
>>>   call_single_queue was initialized or not, and just return if not
>>>   initialized.
>>> 
>>> Signed-off-by: Takao Indoh <indou.takao@jp.fujitsu.com>
>>> ---
>>>  include/linux/smp.h |    5 ++++-
>>>  init/main.c         |    1 +
>>>  kernel/smp.c        |    5 +----
>>>  3 files changed, 6 insertions(+), 5 deletions(-)
>>> 
>>> diff --git a/include/linux/smp.h b/include/linux/smp.h
>>> index 74243c8..4fb3eac 100644
>>> --- a/include/linux/smp.h
>>> +++ b/include/linux/smp.h
>>> @@ -85,12 +85,15 @@ int smp_call_function_any(const struct cpumask *mask,
>>>   * Generic and arch helpers
>>>   */
>>>  #ifdef CONFIG_USE_GENERIC_SMP_HELPERS
>>> +void __init call_function_init(void);
>>>  void generic_smp_call_function_single_interrupt(void);
>>>  void generic_smp_call_function_interrupt(void);
>>>  void ipi_call_lock(void);
>>>  void ipi_call_unlock(void);
>>>  void ipi_call_lock_irq(void);
>>>  void ipi_call_unlock_irq(void);
>>> +#else
>>> +static inline void call_function_init(void) { }
>>>  #endif
>>>  
>>>  /*
>>> @@ -144,7 +147,7 @@ static inline void smp_send_reschedule(int cpu) { }
>>>  #define smp_prepare_boot_cpu()			do {} while (0)
>>>  #define smp_call_function_many(mask, func, info, wait) \
>>>  			(up_smp_call_function(func, info))
>>> -static inline void init_call_single_data(void) { }
>>> +static inline void call_function_init(void) { }
>>>  
>>>  static inline int
>>>  smp_call_function_any(const struct cpumask *mask, smp_call_func_t func,
>>> diff --git a/init/main.c b/init/main.c
>>> index 4a9479e..12821d1 100644
>>> --- a/init/main.c
>>> +++ b/init/main.c
>>> @@ -539,6 +539,7 @@ asmlinkage void __init start_kernel(void)
>>>  	timekeeping_init();
>>>  	time_init();
>>>  	profile_init();
>>> +	call_function_init();
>>
>>Takao,
>>
>>So by calling this function before we enable interrupts we have made
>>sure that per cpu call_single_queue has been initialized and q->list
>>also has been initiliazed and it is an empty list now.
>>
>>After enabling the interrupts, I am assuming we will call
>>generic_smp_call_function_single_interrupt().
>>
>>this function does.
>>
>>        raw_spin_lock(&q->lock);
>>        list_replace_init(&q->list, &list);
>>        raw_spin_unlock(&q->lock);
>>
>>        while (!list_empty(&list)) {
>>                struct call_single_data *data;
>>
>>                data = list_entry(list.next, struct call_single_data,
>>list);
>>                list_del(&data->list);
>>
>>Looking at the code of list_replace_init(), I think we will have odd
>>results if q->list is empty. Looks like list->next will be pointing to
>>&q->list?
>>
>>IIUC, q->list sould be empty when we get pending IPI from previous kernel
>>because any function scheduled for execution must have been inserted on
>>previous kernel's data structures and here we are building fresh data
>>structures.
>>
>>If that is the case, I think above code should have weared interaction.
>>We should think that "list" is not empty and try to execute a data item
>>q->list which is actually not a data item.
>>
>>What am I missing here. After your patch, have to debugged it and 
>>noticed how list_replace_init() does on empty lists and what's the
>>result of list_empty(list)?
>
>When list_replace_init(&q->list, &list) is called,
>they are changed as followed.
>
>/* list_replace */
>(A) &list->next = &q->list->next;
>(B) &list->next->prev = &list;
>(C) &list->prev = &q->list->prev;
>(D) &list->prev->next = &list;
>
>/* INIT_LIST_HEAD */
>(E) &q->list->next = &q->list;
>(F) &q->list->prev = &q->list;
>
>So, if q->list is empty, each list is changed like this.
>
>(Initial state)
>list.next ==> &list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &q->list
>
>(A)
>list.next ==> &q->list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &q->list
>
>(B)
>list.next ==> &q->list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &list
>
>(C)
>list.next ==> &q->list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &list
>
>(D)
>list.next ==> &list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &list
>
>(E)
>list.next ==> &list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &list
>
>(F)
>list.next ==> &list
>list.prev ==> &list
>q->list.next ==> &q->list
>q->list.prev ==> &q->list
>
>
>So, list_empty(list)? is always false, if I am not missing something.

No, list_empty(list)? is always *true*.

Thanks,
Takao Indoh



>>
>>Thanks
>>Vivek
>> 
>>
>>
>>>  	if (!irqs_disabled())
>>>  		printk(KERN_CRIT "start_kernel(): bug: interrupts were "
>>>  				 "enabled early\n");
>>> diff --git a/kernel/smp.c b/kernel/smp.c
>>> index 73a1951..fb67dfa 100644
>>> --- a/kernel/smp.c
>>> +++ b/kernel/smp.c
>>> @@ -74,7 +74,7 @@ static struct notifier_block __cpuinitdata 
>>> hotplug_cfd_notifier = {
>>>  	.notifier_call		= hotplug_cfd,
>>>  };
>>>  
>>> -static int __cpuinit init_call_single_data(void)
>>> +void __init call_function_init(void)
>>>  {
>>>  	void *cpu = (void *)(long)smp_processor_id();
>>>  	int i;
>>> @@ -88,10 +88,7 @@ static int __cpuinit init_call_single_data(void)
>>>  
>>>  	hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
>>>  	register_cpu_notifier(&hotplug_cfd_notifier);
>>> -
>>> -	return 0;
>>>  }
>>> -early_initcall(init_call_single_data);
>>>  
>>>  /*
>>>   * csd_lock/csd_unlock used to serialize access to per-cpu csd resources

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