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

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Date:   Sun, 29 Jan 2023 09:13:55 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Zhong Jinghua <zhongjinghua@...wei.com>
Cc:     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, 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.

Thanks,
Kuai
> 
> This isn't ok, sorry.
> 
> greg k-h
> .
>