linux-kernel - Re: [PATCH] scsi: sd: call device_del() if device_add

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Message-ID: <20220331054156.GI3293@kadam>
Date:   Thu, 31 Mar 2022 08:41:56 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Wenchao Hao <haowenchao@...wei.com>
Cc:     fmdefrancesco@...il.com, axboe@...nel.dk, jejb@...ux.ibm.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, martin.petersen@...cle.com,
        syzbot+f08c77040fa163a75a46@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com, linfeilong@...wei.com
Subject: Re: [PATCH] scsi: sd: call device_del() if device_add_disk() fails

On Thu, Mar 31, 2022 at 11:26:22AM -0400, 'Wenchao Hao' via syzkaller-bugs wrote:
> I do not think it's necessary to call device_del() on this path. If the device
> has been added, put_device() would delete it from sysfs. So the origin error
> handle is ok with me.
> 

No.  The original is buggy and it was detected at runtime by syzbot.
It's not static analysis, it is an actual bug found in testing.

The device_put() unwinds device_initialize().  The device_del() unwinds
device_add().  Take a look at the comments to device_add() or take a
look at how device_register/unregister() work.

The temptation was to call device_unregister() which is a combined
device_del(); device_put(); but when the device_initialize() and
device_add() are called separately, then I think it is more readable to
call del and put separately as well.

regards,
dan carpenter