linux-kernel - Re: [PATCH v5 1/3] scsi: core: Add new helper to iterate all devices of host

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Message-ID: <cb9b64a1-4c51-481a-ae5a-c20df70360ea@gmail.com>
Date: Thu, 13 Jun 2024 15:10:14 +0800
From: Wenchao Hao <haowenchao22@...il.com>
To: Hannes Reinecke <hare@...e.de>,
 "James E . J . Bottomley" <James.Bottomley@...senPartnership.com>,
 "Martin K . Petersen" <martin.petersen@...cle.com>,
 linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] scsi: core: Add new helper to iterate all devices
 of host

On 2024/6/13 14:27, Hannes Reinecke wrote:
> On 6/12/24 17:06, Wenchao Hao wrote:
>> On 6/12/24 4:33 PM, Hannes Reinecke wrote:
>>> On 6/5/24 11:17, Wenchao Hao wrote:
>>>> shost_for_each_device() would skip devices which is in SDEV_CANCEL or
>>>> SDEV_DEL state, for some scenarios, we donot want to skip these 
>>>> devices,
>>>> so add a new macro shost_for_each_device_include_deleted() to handle 
>>>> it.
>>>>
>>>> Following changes are introduced:
>>>>
>>>> 1. Rework scsi_device_get(), add new helper __scsi_device_get() which
>>>>      determine if skip deleted scsi_device by parameter "skip_deleted".
>>>> 2. Add new parameter "skip_deleted" to __scsi_iterate_devices() which
>>>>      is used when calling __scsi_device_get()
>>>> 3. Update shost_for_each_device() to call __scsi_iterate_devices() with
>>>>      "skip_deleted" true
>>>> 4. Add new macro shost_for_each_device_include_deleted() which call
>>>>      __scsi_iterate_devices() with "skip_deleted" false
>>>>
>>>> Signed-off-by: Wenchao Hao <haowenchao22@...il.com>
>>>> ---
>>>>    drivers/scsi/scsi.c        | 46 
>>>> ++++++++++++++++++++++++++------------
>>>>    include/scsi/scsi_device.h | 25 ++++++++++++++++++---
>>>>    2 files changed, 54 insertions(+), 17 deletions(-)
>>>>
>>>> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
>>>> index 3e0c0381277a..5913de543d93 100644
>>>> --- a/drivers/scsi/scsi.c
>>>> +++ b/drivers/scsi/scsi.c
>>>> @@ -735,20 +735,18 @@ int scsi_cdl_enable(struct scsi_device *sdev, 
>>>> bool enable)
>>>>        return 0;
>>>>    }
>>>>    -/**
>>>> - * scsi_device_get  -  get an additional reference to a scsi_device
>>>> +/*
>>>> + * __scsi_device_get  -  get an additional reference to a scsi_device
>>>>     * @sdev:    device to get a reference to
>>>> - *
>>>> - * Description: Gets a reference to the scsi_device and increments 
>>>> the use count
>>>> - * of the underlying LLDD module.  You must hold host_lock of the
>>>> - * parent Scsi_Host or already have a reference when calling this.
>>>> - *
>>>> - * This will fail if a device is deleted or cancelled, or when the 
>>>> LLD module
>>>> - * is in the process of being unloaded.
>>>> + * @skip_deleted: when true, would return failed if device is deleted
>>>>     */
>>>> -int scsi_device_get(struct scsi_device *sdev)
>>>> +static int __scsi_device_get(struct scsi_device *sdev, bool 
>>>> skip_deleted)
>>>>    {
>>>> -    if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == 
>>>> SDEV_CANCEL)
>>>> +    /*
>>>> +     * if skip_deleted is true and device is in removing, return 
>>>> failed
>>>> +     */
>>>> +    if (skip_deleted &&
>>>> +        (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == 
>>>> SDEV_CANCEL))
>>>>            goto fail;
>>>
>>> Nack.
>>> SDEV_DEL means the device is about to be deleted, so we _must not_ 
>>> access it at all.
>>>
>>
>> Sorry I added SDEV_DEL here at hand without understanding what it means.
>> Actually, just include scsi_device which is in SDEV_CANCEL would fix the
>> issues I described.
>>
>> The issues are because device removing concurrent with error handle.
>> Normally, error handle would not be triggered when scsi_device is in
>> SDEV_DEL. Below is my analysis, if it is wrong, please correct me.
>>
>> If there are scsi_cmnd remain unfinished when removing scsi_device,
>> the removing process would waiting for all commands to be finished.
>> If commands error happened and trigger error handle, the removing
>> process would be blocked until error handle finished, because
>> __scsi_remove_device called  del_gendisk() which would wait all
>> requests to be finished. So now scsi_device is in SDEV_CANCEL.
>>
>> If the scsi_device is already in SDEV_DEL, then no scsi_cmnd has been
>> dispatched to this scsi_device, then error handle would never triggered.
>>
>> I want to change the new function __scsi_device_get() as following,
>> please help to review.
>>
>> /*
>>   * __scsi_device_get  -  get an additional reference to a scsi_device
>>   * @sdev:    device to get a reference to
>>   * @skip_canceled: when true, would return failed if device is deleted
>>   */
>> static int __scsi_device_get(struct scsi_device *sdev, bool 
>> skip_canceled)
>> {
>>     /*
>>      * if skip_canceled is true and device is in removing, return failed
>>      */
>>     if (sdev->sdev_state == SDEV_DEL ||
>>         (sdev->sdev_state == SDEV_CANCEL && skip_canceled))
>>         goto fail;
>>     if (!try_module_get(sdev->host->hostt->module))
>>         goto fail;
>>     if (!get_device(&sdev->sdev_gendev))
>>         goto fail_put_module;
>>     return 0;
>>
>> fail_put_module:
>>     module_put(sdev->host->hostt->module);
>> fail:
>>     return -ENXIO;
>> }
>>
> I don't think that's required.
> With your above analysis, wouldn't the problem be solved with:
> 
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 775df00021e4..911fcfa80d69 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -1470,6 +1470,8 @@ void __scsi_remove_device(struct scsi_device *sdev)
>          if (sdev->sdev_state == SDEV_DEL)
>                  return;
> 
> +       scsi_block_when_processing_errors(sdev);
> +
>          if (sdev->is_visible) {
>                  /*
>                   * If scsi_internal_target_block() is running 
> concurrently,
> 
> Hmm?
> 

We can not make sure no scsi_cmnd remain unfinished after 
scsi_block_when_processing_errors(). For example, there is a
command has been dispatched but it's not timeouted when removing
device, no error happened. After scsi_device is set to SDEV_CANCEL,
the removing process would be blocked by del_gendisk() because there
is still a request.

Then the request timeout and abort failed, error handle would be 
triggered, now scsi_device is SDEV_CANCEL.

The error handle would skip this scsi_device when doing device reset.

> Cheers,
> 
> Hannes