Re: [PATCH RFC 2/2] scsi_proc: Change /proc/scsi/scsi to use bus device iterator

From: Hannes Reinecke <hare@suse.de>
To: "Ewan D. Milne" <emilne@redhat.com>, linux-scsi@vger.kernel.org
Subject: Re: [PATCH RFC 2/2] scsi_proc: Change /proc/scsi/scsi to use bus device iterator
Date: Fri, 18 Dec 2015 10:23:26 +0100	[thread overview]
Message-ID: <5673D08E.3040202@suse.de> (raw)
In-Reply-To: <1449583704-32400-3-git-send-email-emilne@redhat.com>

On 12/08/2015 03:08 PM, Ewan D. Milne wrote:
> From: "Ewan D. Milne" <emilne@redhat.com>
>
> This prevents crashing due to accessing a removed element on the list,
> the iterator will now hold the correct reference.  It was not sufficient
> to rely on the klist's reference on the containing device object.
>
>  From a patch originally developed by David Jeffery <djeffery@redhat.com>
>
> Signed-off-by: Ewan D. Milne <emilne@redhat.com>
> ---
>   drivers/scsi/scsi_proc.c | 49 ++++++++++++++++++++++++++++--------------------
>   1 file changed, 29 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/scsi/scsi_proc.c b/drivers/scsi/scsi_proc.c
> index 251598e..6c1b79d 100644
> --- a/drivers/scsi/scsi_proc.c
> +++ b/drivers/scsi/scsi_proc.c
> @@ -40,6 +40,11 @@
>   /* 4K page size, but our output routines, use some slack for overruns */
>   #define PROC_BLOCK_SIZE (3*1024)
>
> +struct scsi_proc_state {
> +	struct klist_iter iter;
> +	int pos;
> +};
> +
>   static struct proc_dir_entry *proc_scsi;
>
>   /* Protect sht->present and sht->proc_dir */
> @@ -370,47 +375,50 @@ static ssize_t proc_scsi_write(struct file *file, const char __user *buf,
>   	return err;
>   }
>
> -static int always_match(struct device *dev, void *data)
> -{
> -	return 1;
> -}
> -
> -static inline struct device *next_scsi_device(struct device *start)
> -{
> -	struct device *next = bus_find_device(&scsi_bus_type, start, NULL,
> -					      always_match);
> -	put_device(start);
> -	return next;
> -}
> -
>   static void *scsi_seq_start(struct seq_file *sfile, loff_t *pos)
>   {
> +	struct scsi_proc_state *state = sfile->private;
>   	struct device *dev = NULL;
>   	loff_t n = *pos;
> +	int err;
> +
> +	err = bus_device_iter_init(&state->iter, &scsi_bus_type);
> +	if (err < 0)
> +		return ERR_PTR(err);
>
> -	while ((dev = next_scsi_device(dev))) {
> +	while ((dev = bus_device_iter_next(&state->iter))) {
>   		if (!n--)
>   			break;
> -		sfile->private++;
> +		put_device(dev);
> +		state->pos++;
>   	}
>   	return dev;
>   }
>
>   static void *scsi_seq_next(struct seq_file *sfile, void *v, loff_t *pos)
>   {
> +	struct scsi_proc_state *state = sfile->private;
> +
>   	(*pos)++;
> -	sfile->private++;
> -	return next_scsi_device(v);
> +	put_device(v);
> +	state->pos++;
> +
> +	return bus_device_iter_next(&state->iter);
>   }
>
>   static void scsi_seq_stop(struct seq_file *sfile, void *v)
>   {
> +	struct scsi_proc_state *state = sfile->private;
> +
>   	put_device(v);
> +	bus_device_iter_exit(&state->iter);
>   }
>
>   static int scsi_seq_show(struct seq_file *sfile, void *dev)
>   {
> -	if (!sfile->private)
> +	struct scsi_proc_state *state = sfile->private;
> +
> +	if (!state->pos)
>   		seq_puts(sfile, "Attached devices:\n");
>
>   	return proc_print_scsidevice(dev, sfile);
> @@ -436,7 +444,8 @@ static int proc_scsi_open(struct inode *inode, struct file *file)
>   	 * We don't really need this for the write case but it doesn't
>   	 * harm either.
>   	 */
> -	return seq_open(file, &scsi_seq_ops);
> +	return seq_open_private(file, &scsi_seq_ops,
> +				sizeof(struct scsi_proc_state));
>   }
>
>   static const struct file_operations proc_scsi_operations = {
> @@ -445,7 +454,7 @@ static const struct file_operations proc_scsi_operations = {
>   	.read		= seq_read,
>   	.write		= proc_scsi_write,
>   	.llseek		= seq_lseek,
> -	.release	= seq_release,
> +	.release	= seq_release_private,
>   };
>
>   /**
>
Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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