Re: [PATCH 6/7] ipmi: Handle queued messages more certainly on panic

[Corey Minyard]

On 08/17/2015 08:59 PM, æåèå / KAWAIïHIDEHIRO wrote:
> Hello Corey,
>
>> -----Original Message-----
>> From: Corey Minyard [mailto:tcminyard@xxxxxxxxx] On Behalf Of Corey Minyard
>> Sent: Wednesday, August 12, 2015 1:13 PM
>> To: æåèå / KAWAIïHIDEHIRO
>> Cc: openipmi-developer@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
>> Subject: Re: [PATCH 6/7] ipmi: Handle queued messages more certainly on panic
>>
>> On 07/27/2015 12:55 AM, Hidehiro Kawai wrote:
>>> panic_event() called as a panic notifier tries to flush queued
>>> messages, but it can't handle them if the kernel panic happens
>>> while processing a message.  What happens depends on when the
>>> kernel panics.
>> Sorry this took so long, I've been traveling.
> No problem.
>
>> I have queued the patches before this one.  They all look good and
>> necessary.
> Thank you for reviewing!
>  
>> I'm not so sure about this patch.  It looks like the only thing that is
>> a real issue is #2 below.
>> It's not so important to avoid dropping messages.
> Initially I thought dropping middle of queued messages breaks
> some consistencies if a message depends on the preceding dropped
> message.  However, userland tools normally issue request messages
> in sequential manner, so the above situation wouldn't happen.
> Now, I think dropping a message is OK.
>
>> Can this be simplified somehow to work around the issue at panic time if
>> intf->curr_msg is set and smi_info->waiting_msg is not?
> There are two cases where intf->curr_msg is set and
> smi_info->waiting_msg is not; one is before (2) and the other
> is after (3).  If we decide to drop intf->curr_msg in both cases,
> I can simplify this patch somewhat.

Yes, please do.

-corey

> Regards,
>
> Hidehiro Kawai
> Hitachi, Ltd. Research & Development Group
>
>> Thank you,
>>
>> -corey
>>
>>> Here is the summary of message sending process.
>>>
>>>     smi_send()
>>>      smi_add_send_msg()
>>> (1)   intf->curr_msg = msg
>>>      sender()
>>> (2)   smi_info->waiting_msg = msg
>>>
>>>     <asynchronously called>
>>>     check_start_timer_thread()
>>>      start_next_msg()
>>>       smi_info->curr_msg = smi_info->waiting_msg
>>> (3)   smi_info->waiting_msg = NULL
>>> (4)   smi_info->handlers->start_transaction()
>>>
>>>     <asynchronously called>
>>>     smi_event_handler()
>>> (5)  handle_transaction_done()
>>>       smi_info->curr_msg = NULL
>>>       deliver_recv_msg()
>>>        ipmi_smi_msg_received()
>>>         intf->curr_msg = NULL
>>>
>>> If the kernel panics before (1), the requested message will be
>>> lost.  But it can't be helped.
>>>
>>> If the kernel panics before (2), new message sent by
>>> send_panic_events() is queued to intf->xmit_msgs because
>>> intf->curr_msg is non-NULL.  But the new message will be never
>>> sent because no one sends intf->curr_msg.  As the result, the
>>> kernel hangs up.
>>>
>>> If the kernel panics before (3), intf->curr_msg will be sent by
>>> set_run_to_completion().  It's no problem.
>>>
>>> If the kernel panics before (4), intf->curr_msg will be lost.
>>> However, messages on intf->xmit_msgs will be handled.
>>>
>>> If the kernel panics before (5), we try to continue running the
>>> state machine.  It may successfully complete.
>>>
>>> If the kernel panics after (5), we will miss the response message
>>> handling, but it's not much problem in the panic context.
>>>
>>> This patch tries to handle messages in intf->curr_msg and
>>> intf->xmit_msgs only once without losing them.  To achieve this,
>>> this patch does that:
>>>   - if a message is in intf->curr_msg or intf->xmit_msgs and
>>>     start_transaction() for the message hasn't been done yet,
>>>     resend it
>>>   - if start_transaction() for a message has been called,
>>>     just continue to run the state machine
>>>   - if the transaction has been completed, do nothing
>>>
>>> >From the perspective of implementation, these are done by keeping
>>> smi_info->waiting_msg until start_transaction() is completed and
>>> by keeping new flag IPMI_MSG_RESEND_ON_PANIC just before starting
>>> the state machine.
>>>
>>> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
>>> ---
>>>  drivers/char/ipmi/ipmi_msghandler.c |   36 +++++++++++++++++++++++++++++++++++
>>>  drivers/char/ipmi/ipmi_si_intf.c    |    5 ++++-
>>>  include/linux/ipmi_smi.h            |    5 +++++
>>>  3 files changed, 45 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
>>> index 5a2d9fe..3dcd814 100644
>>> --- a/drivers/char/ipmi/ipmi_msghandler.c
>>> +++ b/drivers/char/ipmi/ipmi_msghandler.c
>>> @@ -1493,6 +1493,8 @@ static struct ipmi_smi_msg *smi_add_send_msg(ipmi_smi_t intf,
>>>  					     struct ipmi_smi_msg *smi_msg,
>>>  					     int priority)
>>>  {
>>> +	smi_msg->flags |= IPMI_MSG_RESEND_ON_PANIC;
>>> +
>>>  	if (intf->curr_msg) {
>>>  		if (priority > 0)
>>>  			list_add_tail(&smi_msg->link, &intf->hp_xmit_msgs);
>>> @@ -4223,6 +4225,7 @@ struct ipmi_smi_msg *ipmi_alloc_smi_msg(void)
>>>  		rv->done = free_smi_msg;
>>>  		rv->user_data = NULL;
>>>  		atomic_inc(&smi_msg_inuse_count);
>>> +		rv->flags = 0;
>>>  	}
>>>  	return rv;
>>>  }
>>> @@ -4531,7 +4534,40 @@ static int panic_event(struct notifier_block *this,
>>>  			spin_unlock(&intf->waiting_rcv_msgs_lock);
>>>
>>>  		intf->run_to_completion = 1;
>>> +restart:
>>>  		intf->handlers->set_run_to_completion(intf->send_info, 1);
>>> +
>>> +		if (intf->curr_msg) {
>>> +			/*
>>> +			 * This can happen if the kernel panics before
>>> +			 * setting msg to smi_info->waiting_msg or while
>>> +			 * processing a response.  For the former case, we
>>> +			 * resend the message by re-queueing it.  For the
>>> +			 * latter case, we simply ignore it because handling
>>> +			 * response is not much meaningful in the panic
>>> +			 * context.
>>> +			 */
>>> +
>>> +			/*
>>> +			 * Since we want to send the current message first,
>>> +			 * re-queue it into the high-prioritized queue.
>>> +			 */
>>> +			if (intf->curr_msg->flags & IPMI_MSG_RESEND_ON_PANIC)
>>> +				list_add(&intf->curr_msg->link,
>>> +					 &intf->hp_xmit_msgs);
>>> +
>>> +			intf->curr_msg = NULL;
>>> +		}
>>> +
>>> +		if (!list_empty(&intf->hp_xmit_msgs) ||
>>> +		    !list_empty(&intf->xmit_msgs)) {
>>> +			/*
>>> +			 * This can happen if the kernel panics while
>>> +			 * processing a response.  Kick the queue and restart.
>>> +			 */
>>> +			smi_recv_tasklet((unsigned long)intf);
>>> +			goto restart;
>>> +		}
>>>  	}
>>>
>>>  #ifdef CONFIG_IPMI_PANIC_EVENT
>>> diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
>>> index 814b7b7..c5c7806 100644
>>> --- a/drivers/char/ipmi/ipmi_si_intf.c
>>> +++ b/drivers/char/ipmi/ipmi_si_intf.c
>>> @@ -383,7 +383,6 @@ static enum si_sm_result start_next_msg(struct smi_info *smi_info)
>>>  		int err;
>>>
>>>  		smi_info->curr_msg = smi_info->waiting_msg;
>>> -		smi_info->waiting_msg = NULL;
>>>  		debug_timestamp("Start2");
>>>  		err = atomic_notifier_call_chain(&xaction_notifier_list,
>>>  				0, smi_info);
>>> @@ -401,6 +400,7 @@ static enum si_sm_result start_next_msg(struct smi_info *smi_info)
>>>  		rv = SI_SM_CALL_WITHOUT_DELAY;
>>>  	}
>>>   out:
>>> +	smi_info->waiting_msg = NULL;
>>>  	return rv;
>>>  }
>>>
>>> @@ -804,6 +804,9 @@ static enum si_sm_result smi_event_handler(struct smi_info *smi_info,
>>>  {
>>>  	enum si_sm_result si_sm_result;
>>>
>>> +	if (smi_info->curr_msg)
>>> +		smi_info->curr_msg->flags &= ~(IPMI_MSG_RESEND_ON_PANIC);
>>> +
>>>   restart:
>>>  	/*
>>>  	 * There used to be a loop here that waited a little while
>>> diff --git a/include/linux/ipmi_smi.h b/include/linux/ipmi_smi.h
>>> index ba57fb1..1200872 100644
>>> --- a/include/linux/ipmi_smi.h
>>> +++ b/include/linux/ipmi_smi.h
>>> @@ -47,6 +47,9 @@
>>>  /* Structure for the low-level drivers. */
>>>  typedef struct ipmi_smi *ipmi_smi_t;
>>>
>>> +/* Flags for flags member of struct ipmi_smi_msg */
>>> +#define IPMI_MSG_RESEND_ON_PANIC	1 /* If set, resend in panic_event() */
>>> +
>>>  /*
>>>   * Messages to/from the lower layer.  The smi interface will take one
>>>   * of these to send. After the send has occurred and a response has
>>> @@ -75,6 +78,8 @@ struct ipmi_smi_msg {
>>>  	/* Will be called when the system is done with the message
>>>  	   (presumably to free it). */
>>>  	void (*done)(struct ipmi_smi_msg *msg);
>>> +
>>> +	int flags;
>>>  };
>>>
>>>  struct ipmi_smi_handlers {
>>>
>>>

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