linux-kernel - Re: [RFC PATCH] scsi, block: fix duplicate bdi name registration crashes

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Date:   Mon, 30 Jan 2017 13:24:52 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     martin.petersen@...cle.com, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Omar Sandoval <osandov@...ndov.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH] scsi, block: fix duplicate bdi name registration
        crashes

Hi Dan,

this looks mostly fine to me.  A few code comments below, but except
for this there is another issue with it:  We still have drivers
that share a single request_queue for multiple gendisks, so I wonder

Also I think you probably want one patch for the block framework,
and one to switch SCSI over to it.

> +struct disk_devt {
> +	struct kref kref;
> +	void (*release)(struct kref *);
> +};
> +
> +static inline void put_disk_devt(struct disk_devt *disk_devt)
> +{
> +	if (disk_devt)
> +		kref_put(&disk_devt->kref, disk_devt->release);
> +}
> +
> +static inline void get_disk_devt(struct disk_devt *disk_devt)
> +{
> +	if (disk_devt)
> +		kref_get(&disk_devt->kref);
> +}

Given that we have a user-supplied release callack I'd much rather get
rid of the kref here, use a normal atomic_t and pass the disk_devt
structure to the release callback then a kref.