linux-kernel - Re: [PATCH v8 2/4] scsi: ufs: Introduce HPB feature

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Date:   Wed, 12 Aug 2020 20:22:48 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     daejun7.park@...sung.com,
        "avri.altman@....com" <avri.altman@....com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "asutoshd@...eaurora.org" <asutoshd@...eaurora.org>,
        "beanhuo@...ron.com" <beanhuo@...ron.com>,
        "stanley.chu@...iatek.com" <stanley.chu@...iatek.com>,
        "cang@...eaurora.org" <cang@...eaurora.org>,
        "tomas.winkler@...el.com" <tomas.winkler@...el.com>,
        ALIM AKHTAR <alim.akhtar@...sung.com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@...sung.com>,
        Sung-Jun Park <sungjun07.park@...sung.com>,
        yongmyung lee <ymhungry.lee@...sung.com>,
        Jinyoung CHOI <j-young.choi@...sung.com>,
        Adel Choi <adel.choi@...sung.com>,
        BoRam Shin <boram.shin@...sung.com>
Subject: Re: [PATCH v8 2/4] scsi: ufs: Introduce HPB feature

On 2020-08-12 20:00, Daejun Park wrote:
> On 2020-08-06 02:11, Daejun Park wrote:
>>> +static int ufshpb_create_sysfs(struct ufs_hba *hba, struct ufshpb_lu *hpb)
>>> +{
>>> +    int ret;
>>> +
>>> +    ufshpb_stat_init(hpb);
>>> +
>>> +    kobject_init(&hpb->kobj, &ufshpb_ktype);
>>> +    mutex_init(&hpb->sysfs_lock);
>>> +
>>> +    ret = kobject_add(&hpb->kobj, kobject_get(&hba->dev->kobj),
>>> +              "ufshpb_lu%d", hpb->lun);
>>> +
>>> +    if (ret)
>>> +        return ret;
>>> +
>>> +    ret = sysfs_create_group(&hpb->kobj, &ufshpb_sysfs_group);
>>> +
>>> +    if (ret) {
>>> +        dev_err(hba->dev, "ufshpb_lu%d create file error\n", hpb->lun);
>>> +        return ret;
>>> +    }
>>> +
>>> +    dev_info(hba->dev, "ufshpb_lu%d sysfs adds uevent", hpb->lun);
>>> +    kobject_uevent(&hpb->kobj, KOBJ_ADD);
>>> +
>>> +    return 0;
>>> +}
>>
>> Please attach these sysfs attributes to /sys/class/scsi_device/*/device
>> instead of creating a new kobject. Consider using the following
>> scsi_host_template member to define LUN sysfs attributes:
> 
> I am not rejecting your comment. But I added kobject for distinguishing 
> between other attributes and attributes related to HPB feature.
> If you think it's pointless, I'll fix it.

Hi Daejun,

I see two reasons to add these sysfs attributes under
/sys/class/scsi_device/*/device:
- This makes the behavior of the UFS driver similar to that of other Linux
  SCSI LLD drivers.
- This makes it easier for people who want to write udev rules that read
  from these attributes. Since ufshpb_lu%d is attached to the UFS controller
  it is not clear to me which attributes will appear first in sysfs - the
  SCSI device attributes or the ufshpb_lu%d attributes. If there are only
  SCSI device attributes there is no such ambiguity and hence authors of
  udev rules won't have to worry about this race condition.

>>> +void ufshpb_remove(struct ufs_hba *hba)
>>> +{
>>> +    struct ufshpb_lu *hpb, *n_hpb;
>>> +    struct ufsf_feature_info *ufsf;
>>> +    struct scsi_device *sdev;
>>> +
>>> +    ufsf = &hba->ufsf;
>>> +
>>> +    list_for_each_entry_safe(hpb, n_hpb, &lh_hpb_lu, list_hpb_lu) {
>>> +        ufshpb_set_state(hpb, HPB_FAILED);
>>> +
>>> +        sdev = hpb->sdev_ufs_lu;
>>> +        sdev->hostdata = NULL;
>>> +
>>> +        ufshpb_destroy_region_tbl(hpb);
>>> +
>>> +        list_del_init(&hpb->list_hpb_lu);
>>> +        ufshpb_remove_sysfs(hpb);
>>> +
>>> +        kfree(hpb);
>>> +    }
>>> +
>>> +    dev_info(hba->dev, "ufshpb: remove success\n");
>>> +}
>>
>> Should the code in the body of the above loop perhaps be called from inside
>> ufshcd_slave_destroy()?
> 
> Moving other stuffs in the loop is good idea, but removing attributes is problem.
> To avoid adding new kobject, I will try to use sysfs_merge_group() 
> for adding attributes. To delete merged attributes, sysfs_unmerge_group() 
> should be called. But sysfs_remove_groups() is called before calling ufshcd_slave_destroy().

Hmm ... I don't see why the sdev_groups host template attribute can't be used?

Please don't use sysfs_merge_group() and sysfs_unmerge_group() because that
would create a race condition against udev rules if these functions are called
after the device core has emitted a KOBJ_ADD event.

Thanks,

Bart.