Date:   Thu, 31 Jan 2019 16:38:48 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jason Yan <yanaijie@...wei.com>, <martin.petersen@...cle.com>,
        <jejb@...ux.vnet.ibm.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <zhaohongjiang@...wei.com>, <hare@...e.com>,
        <dan.j.williams@...el.com>, <jthumshirn@...e.de>, <hch@....de>,
        <huangdaode@...ilicon.com>, <chenxiang66@...ilicon.com>,
        <xiexiuqi@...wei.com>, <tj@...nel.org>, <miaoxie@...wei.com>,
        Ewan Milne <emilne@...hat.com>, Tomas Henzl <thenzl@...hat.com>
Subject: Re: [PATCH v2 4/7] scsi: libsas: split the replacement of sas disks
 in two steps

On 31/01/2019 10:29, John Garry wrote:
> On 31/01/2019 02:04, Jason Yan wrote:
>>
>>
>> On 2019/1/31 1:22, John Garry wrote:
>>> On 30/01/2019 08:24, Jason Yan wrote:
>>>> Now if a new device replaced a old device, the sas address will change.
>>>
>>> Hmmm... not if it's a SATA disk, which would have some same invented SAS
>>> address.
>>>
>>
>> Yes, it's only for a SAS disk.
>>
>>>> We unregister the old device and discover the new device in one
>>>> revalidation process. But after we deferred the sas_port_delete(), the
>>>> sas port is not deleted when we registering the new port and device.
>>>> The sas port cannot be added because the name of the new port is the
>>>> same as the old.
>>>>
>>>> Fix this by doing the replacement in two steps. The first revalidation
>>>> only delete the old device and trigger a new revalidation. The second
>>>> revalidation discover the new device. To keep the event processing
>>>> synchronised to the original event,

This change seems ok, but please see below regarding generating the 
bcast events.

>>>
>>> Did I originally suggest this? It seems to needlessly make the code more
>>> complicated.
>>>
>>
>> Yes, my first version was raise a new bcast event, and you said it's not
>> synchronised to the original event.  Shall I get back to that approach?
>
> Not sure. This patch seems to fix something closely related to that in
> "scsi: libsas: fix issue of swapping two sas disks", which I will check
> further.
>

An idea:

So, before the libsas changes to generate dynamic events, when libsas 
was processing a particular event type - like a broadcast event - extra 
events generated by the LLDD were discarded by libsas.

The revalidation process attempted to do all revalidation for the domain 
is a single pass, which was ok. This really did not change.

However, in this revalidation pass, we also clear all expander and PHY 
events.

Maybe this is not the right thing to do. Maybe we should just clear a 
single PHY event per pass, since we're processing each broadcast event 
one-by-one.

Today you will notice that if we remove a disk for example, many 
broadcast events are generated, but only the first broadcast event 
actually does any revalidation.

EOM

>
>>
>>> we wrapped a loop and added a new
>>>> parameter to see if we should revalidate again.
>>>>
>>>> Signed-off-by: Jason Yan <yanaijie@...wei.com>
>>>> CC: chenxiang <chenxiang66@...ilicon.com>
>>>> CC: John Garry <john.garry@...wei.com>
>>>> CC: Johannes Thumshirn <jthumshirn@...e.de>
>>>> CC: Ewan Milne <emilne@...hat.com>
>>>> CC: Christoph Hellwig <hch@....de>
>>>> CC: Tomas Henzl <thenzl@...hat.com>
>>>> CC: Dan Williams <dan.j.williams@...el.com>
>>>> CC: Hannes Reinecke <hare@...e.com>
>>>> ---
>>>>  drivers/scsi/libsas/sas_discover.c | 20 +++++++++++++++-----
>>>>  drivers/scsi/libsas/sas_expander.c | 20 ++++++++++++++------
>>>>  include/scsi/libsas.h              |  2 +-
>>>>  3 files changed, 30 insertions(+), 12 deletions(-)
>>>>
>>>> diff --git a/drivers/scsi/libsas/sas_discover.c
>>>> b/drivers/scsi/libsas/sas_discover.c
>>>> index ffc571a12916..c825c89fbddd 100644
>>>> --- a/drivers/scsi/libsas/sas_discover.c
>>>> +++ b/drivers/scsi/libsas/sas_discover.c
>>>> @@ -498,12 +498,10 @@ static void sas_discover_domain(struct
>>>> work_struct *work)
>>>>           task_pid_nr(current), error);
>>>>  }
>>>>
>>>> -static void sas_revalidate_domain(struct work_struct *work)
>>>> +static void sas_do_revalidate_domain(struct asd_sas_port *port, bool
>>>> *retry)
>>>>  {
>>>> -    struct sas_discovery_event *ev = to_sas_discovery_event(work);
>>>> -    struct asd_sas_port *port = ev->port;
>>>> -    struct sas_ha_struct *ha = port->ha;
>>>>      struct domain_device *ddev = port->port_dev;
>>>> +    struct sas_ha_struct *ha = port->ha;
>>>>
>>>>      /* prevent revalidation from finding sata links in recovery */
>>>>      mutex_lock(&ha->disco_mutex);
>>>> @@ -520,7 +518,7 @@ static void sas_revalidate_domain(struct
>>>> work_struct *work)
>>>>
>>>>      if (ddev && (ddev->dev_type == SAS_FANOUT_EXPANDER_DEVICE ||
>>>>               ddev->dev_type == SAS_EDGE_EXPANDER_DEVICE))
>>>> -        sas_ex_revalidate_domain(ddev);
>>>> +        sas_ex_revalidate_domain(ddev, retry);
>>>>
>>>>      pr_debug("done REVALIDATING DOMAIN on port %d, pid:%d\n",
>>>>           port->id, task_pid_nr(current));
>>>> @@ -532,6 +530,18 @@ static void sas_revalidate_domain(struct
>>>> work_struct *work)
>>>>      sas_probe_devices(port);
>>>>  }
>>>>
>>>> +static void sas_revalidate_domain(struct work_struct *work)
>>>> +{
>>>> +    struct sas_discovery_event *ev = to_sas_discovery_event(work);
>>>> +    struct asd_sas_port *port = ev->port;
>>>> +    bool retry;
>>>> +
>>>> +    do {
>>>> +        retry = false;
>>>> +        sas_do_revalidate_domain(port, &retry);
>>>> +    } while (retry);
>>>> +}
>>>> +
>>>>  /* ---------- Events ---------- */
>>>>
>>>>  static void sas_chain_work(struct sas_ha_struct *ha, struct sas_work
>>>> *sw)
>>>> diff --git a/drivers/scsi/libsas/sas_expander.c
>>>> b/drivers/scsi/libsas/sas_expander.c
>>>> index 5cd720f93f96..cdbf8d8a28bf 100644
>>>> --- a/drivers/scsi/libsas/sas_expander.c
>>>> +++ b/drivers/scsi/libsas/sas_expander.c
>>>> @@ -1994,7 +1994,8 @@ static bool dev_type_flutter(enum
>>>> sas_device_type new, enum sas_device_type old)
>>>>      return false;
>>>>  }
>>>>
>>>> -static int sas_rediscover_dev(struct domain_device *dev, int phy_id,
>>>> bool last)
>>>> +static int sas_unregister(struct domain_device *dev, int phy_id, bool
>>>> last,
>>>> +                  bool *retry)
>>>>  {
>>>>      struct expander_device *ex = &dev->ex_dev;
>>>>      struct ex_phy *phy = &ex->ex_phy[phy_id];
>>>> @@ -2045,7 +2046,12 @@ static int sas_rediscover_dev(struct
>>>> domain_device *dev, int phy_id, bool last)
>>>>          SAS_ADDR(phy->attached_sas_addr));
>>>>      sas_unregister_devs_sas_addr(dev, phy_id, last);
>>>>
>>>> -    return sas_discover_new(dev, phy_id);
>>>> +    /* force the next revalidation find this phy and bring it up */
>>>> +    phy->phy_change_count = -1;
>>>> +    ex->ex_change_count = -1;
>>>> +    *retry = true;
>>>
>>> Ohh, sorry to say, but that's a real hack :)
>>>
>>
>> This is the way sas_resume_port() already in use.
>>
>>> Could we just add a flag for the expander PHY to force a discovery
>>> instead of this?
>>>
>>
>> of course we can add a flag instead of this, but I don't think it worth
>> to do this. We have to change the logic of sas_find_bcast_dev() and
>> sas_find_bcast_phy() to achieve this. Or we have to add a new function
>> to find out which PHY's flag is set.
>>
>>> I assume that you need to do this as the expander PHY change count will
>>> not be modified for the next revalidation (so no discovery on that PHY).
>>>
>>
>> To save one instruction(assign), we have to add two(check and assign)?
>> And how to predict if the PHY change count will be modified or not?
>> It's unnessesary to do this.
>>
>>>> +
>>>> +    return 0;
>>>>  }
>>>>
>>>>  /**
>>>> @@ -2062,7 +2068,8 @@ static int sas_rediscover_dev(struct
>>>> domain_device *dev, int phy_id, bool last)
>>>>   * first phy,for other phys in this port, we add it to the port to
>>>>   * forming the wide-port.
>>>>   */
>>>> -static void sas_rediscover(struct domain_device *dev, const int
>>>> phy_id)
>>>> +static void sas_rediscover(struct domain_device *dev, const int
>>>> phy_id,
>>>> +               bool *retry)
>>>>  {
>>>>      struct expander_device *ex = &dev->ex_dev;
>>>>      struct ex_phy *changed_phy = &ex->ex_phy[phy_id];
>>>> @@ -2087,7 +2094,7 @@ static void sas_rediscover(struct domain_device
>>>> *dev, const int phy_id)
>>>>                  break;
>>>>              }
>>>>          }
>>>> -        res = sas_rediscover_dev(dev, phy_id, last);
>>>> +        res = sas_unregister(dev, phy_id, last, retry);
>>>>      } else
>>>>          res = sas_discover_new(dev, phy_id);
>>>>
>>>> @@ -2098,13 +2105,14 @@ static void sas_rediscover(struct
>>>> domain_device *dev, const int phy_id)
>>>>  /**
>>>>   * sas_ex_revalidate_domain - revalidate the domain
>>>>   * @port_dev: port domain device.
>>>> + * @retry: do we need to revalidate again
>>>>   *
>>>>   * NOTE: this process _must_ quit (return) as soon as any connection
>>>>   * errors are encountered.  Connection recovery is done elsewhere.
>>>>   * Discover process only interrogates devices in order to discover the
>>>>   * domain.
>>>>   */
>>>> -void sas_ex_revalidate_domain(struct domain_device *port_dev)
>>>> +void sas_ex_revalidate_domain(struct domain_device *port_dev, bool
>>>> *retry)
>>>>  {
>>>>      int res;
>>>>      struct domain_device *dev = NULL;
>>>> @@ -2119,7 +2127,7 @@ void sas_ex_revalidate_domain(struct
>>>> domain_device *port_dev)
>>>>              res = sas_find_bcast_phy(dev, &phy_id, i, true);
>>>>              if (phy_id == -1)
>>>>                  break;
>>>> -            sas_rediscover(dev, phy_id);
>>>> +            sas_rediscover(dev, phy_id, retry);
>>>>              i = phy_id + 1;
>>>>          } while (i < ex->num_phys);
>>>>      }
>>>> diff --git a/include/scsi/libsas.h b/include/scsi/libsas.h
>>>> index e557bcb0c266..deb75765e555 100644
>>>> --- a/include/scsi/libsas.h
>>>> +++ b/include/scsi/libsas.h
>>>> @@ -692,7 +692,7 @@ int  sas_discover_root_expander(struct
>>>> domain_device *);
>>>>
>>>>  void sas_init_ex_attr(void);
>>>>
>>>> -void sas_ex_revalidate_domain(struct domain_device *);
>>>> +void sas_ex_revalidate_domain(struct domain_device *port_dev, bool
>>>> *retry);
>>>>
>>>>  void sas_unregister_domain_devices(struct asd_sas_port *port, int
>>>> gone);
>>>>  void sas_init_disc(struct sas_discovery *disc, struct asd_sas_port *);
>>>>
>>>
>>>
>>>
>>> .
>>>
>>
>>
>> .
>>
>
>
>
> .
>

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