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

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Date:   Wed, 29 Nov 2023 12:54:33 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     yangxingui <yangxingui@...wei.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

On 28/11/2023 03:45, yangxingui wrote:
> 
> 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().

ok, so then the change to set ex_phy->port = ex->parent_port looks ok. 
Maybe we can put this in a helper with the sas_port_add_phy() call, as 
it is duplicated in sas_ex_join_wide_port()

Do we also need to set ex_phy->phy_state (like sas_ex_join_wide_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.

Then when we get the proper linkrate later, will we then rediscover and 
set the proper SAS address? I am just wondering if this change is really 
required?

BTW, Even with the change to set ex_phy->port = ex->parent_port, are we 
still joining the host-attached expander phy (19) to a port with SAS 
address == 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,
John