Subject: Re: [PATCH 2/2] ehea: fix mutex and spinlock use

From: Thomas Klein <[email-masked]>
Date: Tue, 16 Sep 2008 11:13:13 +0200

Sebastien Dugue wrote:
> On Mon, 15 Sep 2008 17:18:27 +0200 Thomas Klein <[email-masked]> wrote:
> 
>> NACK!
>>
>> I regret but this patch is wrong. It is not sufficient to only lock
>> the replacement of an old list with a new list. Building up those
>> lists is a 3-step process:
>>
>> 1. Count the number of entries a list will contain and allocate mem
>> 2. Fill the list
>> 3. Replace old list with updated list
>>
>> It's obvious that the contents of the list may not change during this
>> procedure. That means that not only the list build-up procedure must
>> be locked. It must be assured that no function that modifies the list's
>> content can be called while another list update is in progress.
>>
>> Jeff, please revert this patch.
> 
>   OK, your call, you know the code better than I do.
> 
>   But the locking could at least be pushed into ehea_update_firmware_handles()
> and ehea_update_bcmc_registrations() instead of being at each call site.
> 
>   Thanks,
> 
>   Sebastien.
> 

It unfortunately can't. As I already mentioned "it must be assured that no
function that modifies the list's content can be called while another list
update is in progress". This means that for example ehea_broadcast_reg_helper()
may not run during a list update. That's why the locks surround these function
calls as well.

Thomas

>> Thanks
>> Thomas
>>
>>
>>
>> Sebastien Dugue wrote:
>>>   Looks like to me that the ehea_fw_handles.lock mutex and the
>>> ehea_bcmc_regs.lock spinlock are taken much longer than necessary and could
>>> as well be pushed inside the functions that need them
>>> (ehea_update_firmware_handles() and ehea_update_bcmc_registrations())
>>> rather than at each callsite.
>>>
>>> Signed-off-by: Sebastien Dugue <[email-masked]>
>>> ---
>>>  drivers/net/ehea/ehea_main.c |   26 ++++----------------------
>>>  1 files changed, 4 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/drivers/net/ehea/ehea_main.c b/drivers/net/ehea/ehea_main.c
>>> index b70c531..c765ec6 100644
>>> --- a/drivers/net/ehea/ehea_main.c
>>> +++ b/drivers/net/ehea/ehea_main.c
>>> @@ -219,9 +219,11 @@ static void ehea_update_firmware_handles(void)
>>>  	}
>>>  
>>>  out_update:
>>> +	mutex_lock(&ehea_fw_handles.lock);
>>>  	kfree(ehea_fw_handles.arr);
>>>  	ehea_fw_handles.arr = arr;
>>>  	ehea_fw_handles.num_entries = i;
>>> +	mutex_unlock(&ehea_fw_handles.lock);
>>>  }
>>>  
>>>  static void ehea_update_bcmc_registrations(void)
>>> @@ -293,9 +295,11 @@ static void ehea_update_bcmc_registrations(void)
>>>  	}
>>>  
>>>  out_update:
>>> +	spin_lock(&ehea_bcmc_regs.lock);
>>>  	kfree(ehea_bcmc_regs.arr);
>>>  	ehea_bcmc_regs.arr = arr;
>>>  	ehea_bcmc_regs.num_entries = i;
>>> +	spin_unlock(&ehea_bcmc_regs.lock);
>>>  }
>>>  
>>>  static struct net_device_stats *ehea_get_stats(struct net_device *dev)
>>> @@ -1770,8 +1774,6 @@ static int ehea_set_mac_addr(struct net_device *dev, void *sa)
>>>  
>>>  	memcpy(dev->dev_addr, mac_addr->sa_data, dev->addr_len);
>>>  
>>> -	spin_lock(&ehea_bcmc_regs.lock);
>>> -
>>>  	/* Deregister old MAC in pHYP */
>>>  	if (port->state == EHEA_PORT_UP) {
>>>  		ret = ehea_broadcast_reg_helper(port, H_DEREG_BCMC);
>>> @@ -1792,7 +1794,6 @@ static int ehea_set_mac_addr(struct net_device *dev, void *sa)
>>>  
>>>  out_upregs:
>>>  	ehea_update_bcmc_registrations();
>>> -	spin_unlock(&ehea_bcmc_regs.lock);
>>>  out_free:
>>>  	kfree(cb0);
>>>  out:
>>> @@ -1954,8 +1955,6 @@ static void ehea_set_multicast_list(struct net_device *dev)
>>>  	}
>>>  	ehea_promiscuous(dev, 0);
>>>  
>>> -	spin_lock(&ehea_bcmc_regs.lock);
>>> -
>>>  	if (dev->flags & IFF_ALLMULTI) {
>>>  		ehea_allmulti(dev, 1);
>>>  		goto out;
>>> @@ -1985,7 +1984,6 @@ static void ehea_set_multicast_list(struct net_device *dev)
>>>  	}
>>>  out:
>>>  	ehea_update_bcmc_registrations();
>>> -	spin_unlock(&ehea_bcmc_regs.lock);
>>>  	return;
>>>  }
>>>  
>>> @@ -2466,8 +2464,6 @@ static int ehea_up(struct net_device *dev)
>>>  	if (port->state == EHEA_PORT_UP)
>>>  		return 0;
>>>  
>>> -	mutex_lock(&ehea_fw_handles.lock);
>>> -
>>>  	ret = ehea_port_res_setup(port, port->num_def_qps,
>>>  				  port->num_add_tx_qps);
>>>  	if (ret) {
>>> @@ -2504,8 +2500,6 @@ static int ehea_up(struct net_device *dev)
>>>  		}
>>>  	}
>>>  
>>> -	spin_lock(&ehea_bcmc_regs.lock);
>>> -
>>>  	ret = ehea_broadcast_reg_helper(port, H_REG_BCMC);
>>>  	if (ret) {
>>>  		ret = -EIO;
>>> @@ -2527,10 +2521,8 @@ out:
>>>  		ehea_info("Failed starting %s. ret=%i", dev->name, ret);
>>>  
>>>  	ehea_update_bcmc_registrations();
>>> -	spin_unlock(&ehea_bcmc_regs.lock);
>>>  
>>>  	ehea_update_firmware_handles();
>>> -	mutex_unlock(&ehea_fw_handles.lock);
>>>  
>>>  	return ret;
>>>  }
>>> @@ -2580,9 +2572,6 @@ static int ehea_down(struct net_device *dev)
>>>  	if (port->state == EHEA_PORT_DOWN)
>>>  		return 0;
>>>  
>>> -	mutex_lock(&ehea_fw_handles.lock);
>>> -
>>> -	spin_lock(&ehea_bcmc_regs.lock);
>>>  	ehea_drop_multicast_list(dev);
>>>  	ehea_broadcast_reg_helper(port, H_DEREG_BCMC);
>>>  
>>> @@ -2591,7 +2580,6 @@ static int ehea_down(struct net_device *dev)
>>>  	port->state = EHEA_PORT_DOWN;
>>>  
>>>  	ehea_update_bcmc_registrations();
>>> -	spin_unlock(&ehea_bcmc_regs.lock);
>>>  
>>>  	ret = ehea_clean_all_portres(port);
>>>  	if (ret)
>>> @@ -2599,7 +2587,6 @@ static int ehea_down(struct net_device *dev)
>>>  			  dev->name, ret);
>>>  
>>>  	ehea_update_firmware_handles();
>>> -	mutex_unlock(&ehea_fw_handles.lock);
>>>  
>>>  	return ret;
>>>  }
>>> @@ -3378,7 +3365,6 @@ static int __devinit ehea_probe_adapter(struct of_device *dev,
>>>  		ehea_error("Invalid ibmebus device probed");
>>>  		return -EINVAL;
>>>  	}
>>> -	mutex_lock(&ehea_fw_handles.lock);
>>>  
>>>  	adapter = kzalloc(sizeof(*adapter), GFP_KERNEL);
>>>  	if (!adapter) {
>>> @@ -3462,7 +3448,6 @@ out_free_ad:
>>>  
>>>  out:
>>>  	ehea_update_firmware_handles();
>>> -	mutex_unlock(&ehea_fw_handles.lock);
>>>  	return ret;
>>>  }
>>>  
>>> @@ -3481,8 +3466,6 @@ static int __devexit ehea_remove(struct of_device *dev)
>>>  
>>>  	flush_scheduled_work();
>>>  
>>> -	mutex_lock(&ehea_fw_handles.lock);
>>> -
>>>  	ibmebus_free_irq(adapter->neq->attr.ist1, adapter);
>>>  	tasklet_kill(&adapter->neq_tasklet);
>>>  
>>> @@ -3492,7 +3475,6 @@ static int __devexit ehea_remove(struct of_device *dev)
>>>  	kfree(adapter);
>>>  
>>>  	ehea_update_firmware_handles();
>>> -	mutex_unlock(&ehea_fw_handles.lock);
>>>  
>>>  	return 0;
>>>  }
>>
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