linux-kernel - Re: [PATCH-next v2 2/2] scsi: fix iscsi rescan fails to create block device

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Message-ID: <c09ec3d3-9f6f-6bf6-8bb9-583c0c7c909d@huaweicloud.com>
Date:   Sun, 29 Jan 2023 14:55:48 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Yu Kuai <yukuai1@...weicloud.com>
Cc:     Zhong Jinghua <zhongjinghua@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, hare@...e.de, bvanassche@....org,
        emilne@...hat.com, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, yi.zhang@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH-next v2 2/2] scsi: fix iscsi rescan fails to create block
 device

Hi,

在 2023/01/29 14:46, Greg KH 写道:
> On Sun, Jan 29, 2023 at 09:13:55AM +0800, Yu Kuai wrote:
>> Hi, Greg
>>
>> 在 2023/01/28 18:45, Greg KH 写道:
>>>> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
>>>> index cac7c902cf70..a22109cdb8ef 100644
>>>> --- a/drivers/scsi/scsi_sysfs.c
>>>> +++ b/drivers/scsi/scsi_sysfs.c
>>>> @@ -1535,9 +1535,7 @@ static void __scsi_remove_target(struct scsi_target *starget)
>>>>    		if (sdev->channel != starget->channel ||
>>>>    		    sdev->id != starget->id)
>>>>    			continue;
>>>> -		if (sdev->sdev_state == SDEV_DEL ||
>>>> -		    sdev->sdev_state == SDEV_CANCEL ||
>>>> -		    !get_device(&sdev->sdev_gendev))
>>>> +		if (!get_device_unless_zero(&sdev->sdev_gendev))
>>>
>>> If sdev_gendev is 0 here, the object is gone and you are working with
>>> memory that is already freed so something is _VERY_ wrong.
>>
>> In fact, this patch will work:
>>
>> In __scsi_remove_target(), 'host_lock' is held to protect iterating
>> siblings, and object will wait for this lock in
>> scsi_device_dev_release() to remove siblings. Hence sdev will not be
>> freed untill the lock is released.
> 
> Then you got lucky, as that is not how a reference counted object should
> be working (i.e. the reference dropped to 0 and it still be kept alive.)
> 
> Please fix up the scsi logic here, don't abuse the reference count code.
> 

Thanks for the reply, I agree that we should fix this in scsi layer.

Kuai