Re: [PATCH v2] scsi: sd: block: Fix regressions in read-only block device handling

[Hannes Reinecke <hare@suse.de>]

On 2/13/19 3:57 AM, Martin K. Petersen wrote:
> Some devices come online in write protected state and switch to
> read-write once they are ready to process I/O requests. These devices
> broke with commit 20bd1d026aac ("scsi: sd: Keep disk read-only when
> re-reading partition") because we had no way to distinguish between a
> user decision to set a block_device read-only and the actual hardware
> device being write-protected.
> 
> Because partitions are dropped and recreated on revalidate we are
> unable to persist any user-provided policy in hd_struct. Introduce a
> bitmap in struct gendisk to track the user configuration. This bitmap
> is updated when BLKROSET is called on a given disk or partition.
> 
> A helper function, get_user_ro(), is provided to determine whether the
> ioctl has forced read-only state for a given block device. This helper
> is used by set_disk_ro() and add_partition() to ensure that both
> existing and newly created partitions will get the correct state.
> 
>   - If BLKROSET sets a whole disk device read-only, all partitions will
>     now end up in a read-only state.
> 
>   - If BLKROSET sets a given partition read-only, that partition will
>     remain read-only post revalidate.
> 
>   - Otherwise both the whole disk device and any partitions will
>     reflect the write protect state of the underlying device.
> 
> Cc: Jeremy Cline <jeremy@jcline.org>
> Cc: Oleksii Kurochko <olkuroch@cisco.com>
> Cc: stable@vger.kernel.org # v4.16+
> Reported-by: Oleksii Kurochko <olkuroch@cisco.com>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201221
> Fixes: 20bd1d026aac ("scsi: sd: Keep disk read-only when re-reading partition")
> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
> 
> ---
> 
> v2:
> 	- Track user read-only state in a bitmap
> 
> 	- Work around the regression that caused us to drop user
> 	  preferences on revalidate
> ---
>   block/genhd.c             | 22 +++++++++++++++++-----
>   block/ioctl.c             |  4 ++++
>   block/partition-generic.c |  2 +-
>   drivers/scsi/sd.c         |  4 +---
>   include/linux/genhd.h     |  2 ++
>   5 files changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index 1dd8fd6613b8..34667eb1d3cc 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1544,19 +1544,31 @@ void set_device_ro(struct block_device *bdev, int flag)
>   
>   EXPORT_SYMBOL(set_device_ro);
>   
> +bool get_user_ro(struct gendisk *disk, unsigned int partno)
> +{
> +	/* Is the user read-only bit set for the whole disk device? */
> +	if (test_bit(0, disk->user_ro_bitmap))
> +		return true;
> +
> +	/* Is the user read-only bit set for this particular partition? */
> +	if (test_bit(partno, disk->user_ro_bitmap))
> +		return true;
> +
> +	return false;
> +}
> +EXPORT_SYMBOL(get_user_ro);
> +
>   void set_disk_ro(struct gendisk *disk, int flag)
>   {
>   	struct disk_part_iter piter;
>   	struct hd_struct *part;
>   
> -	if (disk->part0.policy != flag) {
> +	if (disk->part0.policy != flag)
>   		set_disk_ro_uevent(disk, flag);
> -		disk->part0.policy = flag;
> -	}
>   
> -	disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
> +	disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY_PART0);
>   	while ((part = disk_part_iter_next(&piter)))
> -		part->policy = flag;
> +		part->policy = get_user_ro(disk, part->partno) ?: flag;
>   	disk_part_iter_exit(&piter);
>   }
>   
> diff --git a/block/ioctl.c b/block/ioctl.c
> index 4825c78a6baa..41206df89485 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -451,6 +451,10 @@ static int blkdev_roset(struct block_device *bdev, fmode_t mode,
>   		return ret;
>   	if (get_user(n, (int __user *)arg))
>   		return -EFAULT;
> +	if (n)
> +		set_bit(bdev->bd_partno, bdev->bd_disk->user_ro_bitmap);
> +	else
> +		clear_bit(bdev->bd_partno, bdev->bd_disk->user_ro_bitmap);
>   	set_device_ro(bdev, n);
>   	return 0;
>   }
> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index 8e596a8dff32..c6a3c21c2496 100644
> --- a/block/partition-generic.c
> +++ b/block/partition-generic.c
> @@ -338,7 +338,7 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
>   		queue_limit_discard_alignment(&disk->queue->limits, start);
>   	p->nr_sects = len;
>   	p->partno = partno;
> -	p->policy = get_disk_ro(disk);
> +	p->policy = get_user_ro(disk, partno) ?: get_disk_ro(disk);
>   
>   	if (info) {
>   		struct partition_meta_info *pinfo = alloc_part_info(disk);
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 67cc439b86e4..5dfe37b08d3b 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2591,10 +2591,8 @@ sd_read_write_protect_flag(struct scsi_disk *sdkp, unsigned char *buffer)
>   	int res;
>   	struct scsi_device *sdp = sdkp->device;
>   	struct scsi_mode_data data;
> -	int disk_ro = get_disk_ro(sdkp->disk);
>   	int old_wp = sdkp->write_prot;
>   
> -	set_disk_ro(sdkp->disk, 0);
>   	if (sdp->skip_ms_page_3f) {
>   		sd_first_printk(KERN_NOTICE, sdkp, "Assuming Write Enabled\n");
>   		return;
> @@ -2632,7 +2630,7 @@ sd_read_write_protect_flag(struct scsi_disk *sdkp, unsigned char *buffer)
>   			  "Test WP failed, assume Write Enabled\n");
>   	} else {
>   		sdkp->write_prot = ((data.device_specific & 0x80) != 0);
> -		set_disk_ro(sdkp->disk, sdkp->write_prot || disk_ro);
> +		set_disk_ro(sdkp->disk, sdkp->write_prot);
>   		if (sdkp->first_scan || old_wp != sdkp->write_prot) {
>   			sd_printk(KERN_NOTICE, sdkp, "Write Protect is %s\n",
>   				  sdkp->write_prot ? "on" : "off");
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 06c0fd594097..9645c2604465 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -194,6 +194,7 @@ struct gendisk {
>   	 */
>   	struct disk_part_tbl __rcu *part_tbl;
>   	struct hd_struct part0;
> +	DECLARE_BITMAP(user_ro_bitmap, DISK_MAX_PARTS);
>   
>   	const struct block_device_operations *fops;
>   	struct request_queue *queue;
> @@ -433,6 +434,7 @@ extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
>   
>   extern void set_device_ro(struct block_device *bdev, int flag);
>   extern void set_disk_ro(struct gendisk *disk, int flag);
> +extern bool get_user_ro(struct gendisk *disk, unsigned int partno);
>   
>   static inline int get_disk_ro(struct gendisk *disk)
>   {
> 
Hmm. Can't say I like it. But as we're dropping partitions on revalidate 
I guess we'll have to do it that way. Oh well.

Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
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