Re: [PATCH v2 7/7] scsi: libsas: fix issue of swapping two sas disks

[Jason Yan <yanaijie@huawei.com>]

On 2019/1/31 1:53, John Garry wrote:
> On 30/01/2019 08:24, Jason Yan wrote:
>> The work flow of revalidation now is scanning expander phy by the
>> sequence of the phy and check if the phy have changed. This will leads
>> to an issue of swapping two sas disks on one expander.
>>
>> Assume we have two sas disks, connected with expander phy10 and phy11:
>>
>> phy10: 5000cca04eb1001d  port-0:0:10
>> phy11: 5000cca04eb043ad  port-0:0:11
>>
>> Swap these two disks, and imaging the following scenario:
>>
>> revalidation 1:
>
> What does "revalidation 1" actually mean?

'revalidation 1' means one entry in sas_discover_domain().

>
>>   -->phy10: 0 --> delete phy10 domain device
>>   -->phy11: 5000cca04eb043ad (no change)
>
> so is disk 11 still inserted at this stage?

Maybe, but that's what we read from the hardware.

>
>> revalidation done
>>
>> revalidation 2:
>
> is port-0:0:10 deleted now?
>

Yes. But we don't care about it.

>>   -->step 1, check phy10:
>>   -->phy10: 5000cca04eb043ad   --> add to wide port(port-0:0:11) (phy11
>>        address is still 5000cca04eb043ad now)
>
> So this should not happen. How are you physcially swapping them such
> that phy11 address is still 5000cca04eb043ad? I don't see how this would
> be true at revalidation 1.
>

This issue is because we always process the PHYs from 0 to max phy 
number. And please be aware of the real physcial address of the PHY and 
the address stored in the memory is not always the same.
Actually when you checking phy10, phy11 physcial address is not 
5000cca04eb043ad. But the address stored in domain device is still 
5000cca04eb043ad. We have not get a chance to to read it because we are 
processing phy10 now, right?

It's very easy to reproduce. I suggest you to do it yourself and look at 
the logs.

>>
>>   -->step 2, check phy11:
>>   -->phy11: 0  --> phy11 address is 0 now, but it's part of wide
>>        port(port-0:0:11), the domain device will not be deleted.
>> revalidation done
>>
>> revalidation 3:
>>   -->phy10, 5000cca04eb043ad (no change)
>>   -->phy11: 5000cca04eb1001d --> try to add port-0:0:11 but failed,
>>        port-0:0:11 already exist, trigger a warning as follows
>> revalidation done
>>
>> [14790.189699] sysfs: cannot create duplicate filename
>> '/devices/pci0000:74/0000:74:02.0/host0/port-0:0/expander-0:0/port-0:0:11'
>>
>> [14790.201081] CPU: 25 PID: 5031 Comm: kworker/u192:3 Not tainted
>> 4.16.0-rc1-191134-g138f084-dirty #228
>> [14790.210199] Hardware name: Huawei D06/D06, BIOS Hisilicon D06 EC UEFI
>> Nemo 2.0 RC0 - B303 05/16/2018
>> [14790.219323] Workqueue: 0000:74:02.0_disco_q sas_revalidate_domain
>> [14790.225404] Call trace:
>> [14790.227842]  dump_backtrace+0x0/0x18c
>> [14790.231492]  show_stack+0x14/0x1c
>> [14790.234798]  dump_stack+0x88/0xac
>> [14790.238101]  sysfs_warn_dup+0x64/0x7c
>> [14790.241751]  sysfs_create_dir_ns+0x90/0xa0
>> [14790.245835]  kobject_add_internal+0xa0/0x284
>> [14790.250092]  kobject_add+0xb8/0x11c
>> [14790.253570]  device_add+0xe8/0x598
>> [14790.256960]  sas_port_add+0x24/0x50
>> [14790.260436]  sas_ex_discover_devices+0xb10/0xc30
>> [14790.265040]  sas_ex_revalidate_domain+0x1d8/0x518
>> [14790.269731]  sas_revalidate_domain+0x12c/0x154
>> [14790.274163]  process_one_work+0x128/0x2b0
>> [14790.278160]  worker_thread+0x14c/0x408
>> [14790.281897]  kthread+0xfc/0x128
>> [14790.285026]  ret_from_fork+0x10/0x18
>> [14790.288598] ------------[ cut here ]------------
>>
>> At last, the disk 5000cca04eb1001d is lost.
>>
>> The basic idea of fix this issue is to let the revalidation first scan
>> all phys, and then unregisterring devices. Only when no devices need to
>> be unregisterred, go to the next step to discover new devices. If there
>> are devices need unregister, unregister those devices and tell the
>> revalidation event processor to retry again. The next revalidation will
>> process the discovering of the new devices.
>>
>> Tested-by: Chen Liangfei <chenliangfei1@huawei.com>
>> Signed-off-by: Jason Yan <yanaijie@huawei.com>
>> CC: Xiaofei Tan <tanxiaofei@huawei.com>
>> CC: chenxiang <chenxiang66@hisilicon.com>
>> CC: John Garry <john.garry@huawei.com>
>> CC: Johannes Thumshirn <jthumshirn@suse.de>
>> CC: Ewan Milne <emilne@redhat.com>
>> CC: Christoph Hellwig <hch@lst.de>
>> CC: Tomas Henzl <thenzl@redhat.com>
>> CC: Dan Williams <dan.j.williams@intel.com>
>> CC: Hannes Reinecke <hare@suse.com>
>> ---
>>  drivers/scsi/libsas/sas_expander.c | 146
>> +++++++++++++++++++++++++------------
>>  1 file changed, 100 insertions(+), 46 deletions(-)
>>
>> diff --git a/drivers/scsi/libsas/sas_expander.c
>> b/drivers/scsi/libsas/sas_expander.c
>> index e781941a7088..073bb5c6e353 100644
>> --- a/drivers/scsi/libsas/sas_expander.c
>> +++ b/drivers/scsi/libsas/sas_expander.c
>> @@ -2056,7 +2056,7 @@ static bool sas_process_flutter(struct
>> domain_device *dev, struct ex_phy *phy,
>>      return true;
>>  }
>>
>> -static int sas_unregister(struct domain_device *dev, int phy_id, bool
>> last,
>> +static int sas_ex_unregister(struct domain_device *dev, int phy_id,
>> bool last,
>>                    bool *retry)
>>  {
>>      struct expander_device *ex = &dev->ex_dev;
>> @@ -2108,21 +2108,8 @@ static int sas_unregister(struct domain_device
>> *dev, int phy_id, bool last,
>>      return 0;
>>  }
>>
>> -/**
>> - * sas_rediscover - revalidate the domain.
>> - * @dev:domain device to be detect.
>> - * @phy_id: the phy id will be detected.
>> - *
>> - * 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.For plugging out, we un-register the device only when it is
>> - * the last phy in the port, for other phys in this port, we just
>> delete it
>> - * from the port.For inserting, we do discovery when it is the
>> - * 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_ex_unregister_device(struct domain_device *dev, const
>> int phy_id,
>>                 bool *retry)
>>  {
>>      struct expander_device *ex = &dev->ex_dev;
>> @@ -2131,31 +2118,70 @@ static void sas_rediscover(struct
>> domain_device *dev, const int phy_id,
>>      int i;
>>      bool last = true;    /* is this the last phy of the port */
>>
>> -    pr_debug("ex %016llx phy%d originated BROADCAST(CHANGE)\n",
>> -         SAS_ADDR(dev->sas_addr), phy_id);
>> -
>> -    if (SAS_ADDR(changed_phy->attached_sas_addr) != 0) {
>> -        for (i = 0; i < ex->num_phys; i++) {
>> -            struct ex_phy *phy = &ex->ex_phy[i];
>> +    for (i = 0; i < ex->num_phys; i++) {
>> +        struct ex_phy *phy = &ex->ex_phy[i];
>>
>> -            if (i == phy_id)
>> -                continue;
>> -            if (SAS_ADDR(phy->attached_sas_addr) ==
>> -                SAS_ADDR(changed_phy->attached_sas_addr)) {
>> -                pr_debug("phy%d part of wide port with phy%d\n",
>> -                     phy_id, i);
>> -                last = false;
>> -                break;
>> -            }
>> +        if (i == phy_id)
>> +            continue;
>> +        if (SAS_ADDR(phy->attached_sas_addr) ==
>> +            SAS_ADDR(changed_phy->attached_sas_addr)) {
>> +            pr_debug("phy%d part of wide port with phy%d\n",
>> +                 phy_id, i);
>> +            last = false;
>> +            break;
>>          }
>> -        res = sas_unregister(dev, phy_id, last, retry);
>> -    } else
>> -        res = sas_discover_new(dev, phy_id);
>> +    }
>> +    res = sas_ex_unregister(dev, phy_id, last, retry);
>>
>>      pr_debug("ex %016llx phy%d discover returned 0x%x\n",
>>           SAS_ADDR(dev->sas_addr), phy_id, res);
>>  }
>>
>> +static int sas_ex_try_unregister(struct domain_device *dev, u8
>> *changed_phy,
>> +                 int nr, bool *retry)
>> +{
>> +    struct expander_device *ex = &dev->ex_dev;
>> +    int unregistered = 0;
>> +    struct ex_phy *phy;
>> +    int i;
>> +
>> +    for (i = 0; i < nr; i++) {
>> +        pr_debug("ex %016llx phy%d originated BROADCAST(CHANGE)\n",
>> +             SAS_ADDR(dev->sas_addr), changed_phy[i]);
>> +
>> +        phy = &ex->ex_phy[changed_phy[i]];
>> +
>> +        if (SAS_ADDR(phy->attached_sas_addr) == 0)
>> +            continue;
>> +
>> +        sas_ex_unregister_device(dev, changed_phy[i], retry);
>> +        changed_phy[i] = 0xff;
>> +        unregistered++;
>> +    }
>> +    return unregistered;
>> +}
>> +
>> +static void sas_ex_register(struct domain_device *dev, u8 *changed_phy,
>> +                int nr)
>> +{
>> +    struct expander_device *ex = &dev->ex_dev;
>> +    struct ex_phy *phy;
>> +    int res = 0;
>> +    int i;
>> +
>> +    for (i = 0; i < nr; i++) {
>> +        if (changed_phy[i] == 0xff)
>> +            continue;
>> +
>> +        phy = &ex->ex_phy[changed_phy[i]];
>> +
>> +        res = sas_discover_new(dev, changed_phy[i]);
>> +
>> +        pr_debug("ex %016llx phy%d register returned 0x%x\n",
>> +             SAS_ADDR(dev->sas_addr), changed_phy[i], res);
>> +    }
>> +}
>> +
>>  /**
>>   * sas_ex_revalidate_domain - revalidate the domain
>>   * @port_dev: port domain device.
>> @@ -2170,21 +2196,49 @@ void sas_ex_revalidate_domain(struct
>> domain_device *port_dev, bool *retry)
>>  {
>>      int res;
>>      struct domain_device *dev = NULL;
>> +    u8 changed_phy[MAX_EXPANDER_PHYS];
>> +    struct expander_device *ex;
>> +    int unregistered = 0;
>> +    int phy_id;
>> +    int nr = 0;
>> +    int i = 0;
>>
>>      res = sas_find_bcast_dev(port_dev, &dev);
>> -    if (res == 0 && dev) {
>> -        struct expander_device *ex = &dev->ex_dev;
>> -        int i = 0, phy_id;
>> -
>> -        do {
>> -            phy_id = -1;
>> -            res = sas_find_bcast_phy(dev, &phy_id, i, true);
>> -            if (phy_id == -1)
>> -                break;
>> -            sas_rediscover(dev, phy_id, retry);
>> -            i = phy_id + 1;
>> -        } while (i < ex->num_phys);
>> +    if (res || !dev)
>> +        return;
>> +
>> +    memset(changed_phy, 0xff, MAX_EXPANDER_PHYS);
>> +    ex = &dev->ex_dev;
>> +
>> +    do {
>> +        phy_id = -1;
>> +        res = sas_find_bcast_phy(dev, &phy_id, i, true);
>> +        if (phy_id == -1)
>> +            break;
>> +        changed_phy[nr++] = phy_id;
>> +        i = phy_id + 1;
>> +    } while (i < dev->ex_dev.num_phys);
>> +
>> +    if (nr == 0)
>> +        return;
>> +
>> +    unregistered = sas_ex_try_unregister(dev, changed_phy, nr, retry);
>> +
>> +    if (unregistered > 0) {
>> +        struct ex_phy *phy;
>> +
>> +        for (i = 0; i < nr; i++) {
>> +            if (changed_phy[i] == 0xff)
>> +                continue;
>> +            phy = &ex->ex_phy[changed_phy[i]];
>> +            phy->phy_change_count = -1;
>> +        }
>> +        ex->ex_change_count = -1;
>> +        *retry = true;
>> +        return;
>>      }
>> +
>> +    sas_ex_register(dev, changed_phy, nr);
>>  }
>>
>>  void sas_smp_handler(struct bsg_job *job, struct Scsi_Host *shost,
>>
>
>
>
> .
>