linux-kernel - Re: [PATCH v4] scsi: libsas: Fix the failure of adding phy with zero-address to port

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Date:   Tue, 28 Nov 2023 11:45:55 +0800
From:   yangxingui <yangxingui@...wei.com>
To:     John Garry <john.g.garry@...cle.com>, <yanaijie@...wei.com>,
        <jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
        <damien.lemoal@...nsource.wdc.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...wei.com>, <prime.zeng@...ilicon.com>,
        <kangfenglong@...wei.com>, <chenxiang66@...ilicon.com>
Subject: Re: [PATCH v4] scsi: libsas: Fix the failure of adding phy with
 zero-address to port

Hi John,

On 2023/11/28 3:28, John Garry wrote:
> On 24/11/2023 02:27, yangxingui wrote:
>>> We already do this in sas_ex_join_wide_port(), right?
>> No, If the addr of ex_phy matches dev->parent, sas_ex_join_wide_port() 
>> will not be called, but sas_add_parent_port() will be called  as follows:
>> static int sas_ex_discover_dev(struct domain_device *dev, int phy_id)
>> {
>>          struct expander_device *ex = &dev->ex_dev;
>>          struct ex_phy *ex_phy = &ex->ex_phy[phy_id];
>>          struct domain_device *child = NULL;
>>          int res = 0;
>>
>>      <...>
>>          /* Parent and domain coherency */
>>          if (!dev->parent && sas_phy_match_port_addr(dev->port, 
>> ex_phy)) {
>>                  sas_add_parent_port(dev, phy_id);
>>                  return 0;
>>          }
>>          if (dev->parent && sas_phy_match_dev_addr(dev->parent, 
>> ex_phy)) {
>>                  sas_add_parent_port(dev, phy_id);
>>                  if (ex_phy->routing_attr == TABLE_ROUTING)
>>                          sas_configure_phy(dev, phy_id, 
>> dev->port->sas_addr, 1);
>>                  return 0;
>>          }
>>      <...>
>> }
>>
>>>
>>> I am not saying that what we do now does not have a problem - I am 
>>> just trying to understand what currently happens
>>
>> ok, because ex_phy->port is not set when calling 
>> sas_add_parent_port(), when deleting phy from the parent wide port, it 
>> is not removed from the phy_list of the parent wide port as follows:
>> static void sas_unregister_devs_sas_addr(struct domain_device *parent,
>>                                           int phy_id, bool last)
>> {
>>      <...>
>>      // Since ex_phy->port is not set, this branch will not be enter
> 
> But then how does this ever work? It is because we follow path 
> sas_rediscover_dev() -> sas_discover_new() -> sas_ex_discover_devices() 
> -> sas_ex_discover_dev() -> sas_add_parent_port(), and not 
> sas_rediscover_dev() -> sas_discover_new() -> sas_ex_join_wide_port()? 
> If so, is that because ephy->sas_attached_phy == 0 in sas_discover_new() 
> -> sas_ex_join_wide_port() and it fails?
> 
> BTW, about something mentioned earlier - adding the phy19 with SAS_ADDR 

Yes,
For phy19, when the phy is attached and added to the parent wide port, 
the path is:
sas_rediscover()
	->sas_discover_new()
		->sas_ex_discover_devices()
			->sas_ex_discover_dev()
				-> sas_add_parent_port().
And the path called when it is removed from parent wide port is:
sas_rediscover()
	->sas_unregister_devs_sas_addr() // The sas address of phy19 becomes 0. 
Since ex_phy->port is NULL, phy19 is not removed from the parent wide 
port's phy_list.

For phy0, it is connected to a new sata device.
sas_rediscover()
	->sas_discover_new()->sas_ex_phy_discover()
							->sas_ex_phy_discover_helper()
								->sas_set_ex_phy() // The device type is stp. Since the linkrate 
is 5 and less than 1.5G, sas_address is set to 0.
						->sas_ex_discover_devices()
							->sas_ex_discover_dev()
								->sas_ex_discover_end_dev()
									->sas_port_alloc() // Create port-7:7:0
									->sas_ex_get_linkrate()
										->sas_port_add_phy() // Try adding phy19 to port->7:7:0, 
triggering BUG()

Thanks,
Xingui
.