linux-kernel - Re: [PATCH V2 1/2] driver core: Add ability to delete device links of unregistered devices

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Message-ID: <f538dda5-6c55-0930-b258-85a3245f06a8@intel.com>
Date:   Fri, 9 Jul 2021 16:18:57 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "open list:TARGET SUBSYSTEM" <linux-scsi@...r.kernel.org>,
        Avri Altman <avri.altman@....com>,
        Bean Huo <huobean@...il.com>, Can Guo <cang@...eaurora.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Bart Van Assche <bvanassche@....org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] driver core: Add ability to delete device links of
 unregistered devices

On 9/07/21 2:28 pm, Rafael J. Wysocki wrote:
> On Fri, Jul 9, 2021 at 8:43 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> Managed device links are deleted by device_del(). However it is possible to
>> add a device link to a consumer before device_add(), and then discover an
>> error prevents the device from being used. In that case normally references
>> to the device would be dropped and the device would be deleted. However the
>> device link holds a reference to the device, so the device link and device
>> remain indefinitely.
>>
>> Amend device link removal to accept removal of a link with an
>> unregistered consumer device.
>>
>> To make that work nicely, the devlink_remove_symlinks() function must be
>> amended to cope with the absence of the consumer's sysfs presence,
>> otherwise sysfs_remove_link() will generate a warning.
>>
>> Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> Fixes: b294ff3e34490 ("scsi: ufs: core: Enable power management for wlun")
>> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>>  drivers/base/core.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>> index ea5b85354526..24bacdb315c6 100644
>> --- a/drivers/base/core.c
>> +++ b/drivers/base/core.c
>> @@ -562,7 +562,8 @@ static void devlink_remove_symlinks(struct device *dev,
>>         struct device *con = link->consumer;
>>         char *buf;
>>
>> -       sysfs_remove_link(&link->link_dev.kobj, "consumer");
>> +       if (device_is_registered(con))
>> +               sysfs_remove_link(&link->link_dev.kobj, "consumer");
> 
> I think that this is needed regardless of the changes in
> device_link_put_kref(), because if somebody decides to delete a
> stateless device link before registering the consumer device,
> sysfs_remove_link() will still complain, won't it?

I would think so.

> 
>>         sysfs_remove_link(&link->link_dev.kobj, "supplier");
>>
>>         len = max(strlen(dev_bus_name(sup)) + strlen(dev_name(sup)),
>> @@ -575,8 +576,10 @@ static void devlink_remove_symlinks(struct device *dev,
>>                 return;
>>         }
>>
>> -       snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
>> -       sysfs_remove_link(&con->kobj, buf);
>> +       if (device_is_registered(con)) {
>> +               snprintf(buf, len, "supplier:%s:%s", dev_bus_name(sup), dev_name(sup));
>> +               sysfs_remove_link(&con->kobj, buf);
>> +       }
> 
> And here too, if I'm not mistaken.
> 
> So in that case it would be better to put the above changes into a
> separate patch and add a Fixes tag to it.

Yes, that makes sense.  I'll send a V3

> 
>>         snprintf(buf, len, "consumer:%s:%s", dev_bus_name(con), dev_name(con));
>>         sysfs_remove_link(&sup->kobj, buf);
>>         kfree(buf);
>> @@ -885,6 +888,8 @@ static void device_link_put_kref(struct device_link *link)
>>  {
>>         if (link->flags & DL_FLAG_STATELESS)
>>                 kref_put(&link->kref, __device_link_del);
>> +       else if (!device_is_registered(link->consumer))
>> +               __device_link_del(&link->kref);
>>         else
>>                 WARN(1, "Unable to drop a managed device link reference\n");
>>  }
>> --
>> 2.17.1
>>