[dm-devel] split hard read-only vs read-only policy v2

[dm-devel] split hard read-only vs read-only policy v2

[Christoph Hellwig]

Hi Jens,

this series resurrects a patch from Martin to properly split the flag
indicating a disk has been set read-only by the hardware vs the userspace
policy set through the BLKROSET ioctl.

This series is based on top of the

   "merge struct block_device and struct hd_struct v4"

series and won't apply to mainline or Jens' for-5.11 tree.

A git tree is available here:

    git://git.infradead.org/users/hch/block.git block-hard-ro

Gitweb:

    http://git.infradead.org/users/hch/block.git/shortlog/refs/heads/block-hard-ro


Changes since v1:
 - don't propagate the policy flag from the whole disk to partitions
 - rebased on top of the merge block_device and hd_struct series

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[dm-devel] [PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Christoph Hellwig]

Commit 20bd1d026aac ("scsi: sd: Keep disk read-only when re-reading
partition") addressed a long-standing problem with user read-only
policy being overridden as a result of a device-initiated revalidate.
The commit has since been reverted due to a regression that left some
USB devices read-only indefinitely.

To fix the underlying problems with revalidate we need to keep track
of hardware state and user policy separately.

The gendisk has been updated to reflect the current hardware state set
by the device driver. This is done to allow returning the device to
the hardware state once the user clears the BLKROSET flag.

The resulting semantics are as follows:

 - If BLKROSET is used to set a whole-disk device read-only, any
   partitions will end up in a read-only state until the user
   explicitly clears the flag.

 - If BLKROSET sets a given partition read-only, that partition will
   remain read-only even if the underlying storage stack initiates a
   revalidate. However, the BLKRRPART ioctl will cause the partition
   table to be dropped and any user policy on partitions will be lost.

 - If BLKROSET has not been set, both the whole disk device and any
   partitions will reflect the current write-protect state of the
   underlying device.

Based on a patch from Martin K. Petersen <martin.petersen@oracle.com>.

Reported-by: Oleksii Kurochko <olkuroch@cisco.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201221
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-core.c        |  2 +-
 block/genhd.c           | 34 +++++++++++++++++++---------------
 block/partitions/core.c |  3 +--
 include/linux/genhd.h   |  6 ++++--
 4 files changed, 25 insertions(+), 20 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index cee568389b7e11..0763d1eb85ce15 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -695,7 +695,7 @@ static inline bool bio_check_ro(struct bio *bio, struct block_device *part)
 {
 	const int op = bio_op(bio);
 
-	if (part->bd_read_only && op_is_write(op)) {
+	if (op_is_write(op) && bdev_read_only(part)) {
 		char b[BDEVNAME_SIZE];
 
 		if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
diff --git a/block/genhd.c b/block/genhd.c
index 565cf36a5f1864..5e746223b6fa0f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1625,31 +1625,35 @@ static void set_disk_ro_uevent(struct gendisk *gd, int ro)
 	kobject_uevent_env(&disk_to_dev(gd)->kobj, KOBJ_CHANGE, envp);
 }
 
-void set_disk_ro(struct gendisk *disk, int flag)
+/**
+ * set_disk_ro - set a gendisk read-only
+ * @disk:	The disk device
+ * @state:	true or false
+ *
+ * This function is used to indicate whether a given disk device should have its
+ * read-only flag set. set_disk_ro() is typically used by device drivers to
+ * indicate whether the underlying physical device is write-protected.
+ */
+void set_disk_ro(struct gendisk *disk, bool read_only)
 {
-	struct disk_part_iter piter;
-	struct block_device *part;
-
-	if (disk->part0->bd_read_only != flag) {
-		set_disk_ro_uevent(disk, flag);
-		disk->part0->bd_read_only = flag;
+	if (read_only) {
+		if (test_and_set_bit(GD_READ_ONLY, &disk->state))
+			return;
+	} else {
+		if (!test_and_clear_bit(GD_READ_ONLY, &disk->state))
+			return;
 	}
-
-	disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY);
-	while ((part = disk_part_iter_next(&piter)))
-		part->bd_read_only = flag;
-	disk_part_iter_exit(&piter);
+	set_disk_ro_uevent(disk, read_only);
 }
-
 EXPORT_SYMBOL(set_disk_ro);
 
 int bdev_read_only(struct block_device *bdev)
 {
 	if (!bdev)
 		return 0;
-	return bdev->bd_read_only;
+	return bdev->bd_read_only ||
+		test_bit(GD_READ_ONLY, &bdev->bd_disk->state);
 }
-
 EXPORT_SYMBOL(bdev_read_only);
 
 /*
diff --git a/block/partitions/core.c b/block/partitions/core.c
index deca253583bd3f..5a9633183343c0 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -194,7 +194,7 @@ static ssize_t part_start_show(struct device *dev,
 static ssize_t part_ro_show(struct device *dev,
 			    struct device_attribute *attr, char *buf)
 {
-	return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_read_only);
+	return sprintf(buf, "%d\n", bdev_read_only(dev_to_bdev(dev)));
 }
 
 static ssize_t part_alignment_offset_show(struct device *dev,
@@ -360,7 +360,6 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
 
 	bdev->bd_start_sect = start;
 	bdev_set_nr_sectors(bdev, len);
-	bdev->bd_read_only = get_disk_ro(disk);
 
 	if (info) {
 		err = -ENOMEM;
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 809aaa32d53cba..a62ccbfac54b48 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -163,6 +163,7 @@ struct gendisk {
 	int flags;
 	unsigned long state;
 #define GD_NEED_PART_SCAN		0
+#define GD_READ_ONLY			1
 	struct kobject *slave_dir;
 
 	struct timer_rand_state *random;
@@ -249,11 +250,12 @@ static inline void add_disk_no_queue_reg(struct gendisk *disk)
 extern void del_gendisk(struct gendisk *gp);
 extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
 
-extern void set_disk_ro(struct gendisk *disk, int flag);
+void set_disk_ro(struct gendisk *disk, bool read_only);
 
 static inline int get_disk_ro(struct gendisk *disk)
 {
-	return disk->part0->bd_read_only;
+	return disk->part0->bd_read_only ||
+		test_bit(GD_READ_ONLY, &disk->state);
 }
 
 extern void disk_block_events(struct gendisk *disk);
-- 
2.29.2

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Re: [dm-devel] [PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Alex Elder]

On 11/29/20 12:19 PM, Christoph Hellwig wrote:
> Commit 20bd1d026aac ("scsi: sd: Keep disk read-only when re-reading
> partition") addressed a long-standing problem with user read-only

Little nit I noticed below.	-Alex

. . .

> diff --git a/block/genhd.c b/block/genhd.c
> index 565cf36a5f1864..5e746223b6fa0f 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1625,31 +1625,35 @@ static void set_disk_ro_uevent(struct gendisk *gd, int ro)
>  	kobject_uevent_env(&disk_to_dev(gd)->kobj, KOBJ_CHANGE, envp);
>  }
>  
> -void set_disk_ro(struct gendisk *disk, int flag)
> +/**
> + * set_disk_ro - set a gendisk read-only
> + * @disk:	The disk device
> + * @state:	true or false

s/state/read_only/

> + *
> + * This function is used to indicate whether a given disk device should have its
> + * read-only flag set. set_disk_ro() is typically used by device drivers to
> + * indicate whether the underlying physical device is write-protected.
> + */
> +void set_disk_ro(struct gendisk *disk, bool read_only)

. . .


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Re: [dm-devel] [PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Hannes Reinecke]

On 11/29/20 7:19 PM, Christoph Hellwig wrote:
> Commit 20bd1d026aac ("scsi: sd: Keep disk read-only when re-reading
> partition") addressed a long-standing problem with user read-only
> policy being overridden as a result of a device-initiated revalidate.
> The commit has since been reverted due to a regression that left some
> USB devices read-only indefinitely.
> 
> To fix the underlying problems with revalidate we need to keep track
> of hardware state and user policy separately.
> 
> The gendisk has been updated to reflect the current hardware state set
> by the device driver. This is done to allow returning the device to
> the hardware state once the user clears the BLKROSET flag.
> 
> The resulting semantics are as follows:
> 
>   - If BLKROSET is used to set a whole-disk device read-only, any
>     partitions will end up in a read-only state until the user
>     explicitly clears the flag.
> 
>   - If BLKROSET sets a given partition read-only, that partition will
>     remain read-only even if the underlying storage stack initiates a
>     revalidate. However, the BLKRRPART ioctl will cause the partition
>     table to be dropped and any user policy on partitions will be lost.
> 
>   - If BLKROSET has not been set, both the whole disk device and any
>     partitions will reflect the current write-protect state of the
>     underlying device.
> 
> Based on a patch from Martin K. Petersen <martin.petersen@oracle.com>.
> 
> Reported-by: Oleksii Kurochko <olkuroch@cisco.com>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201221
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/blk-core.c        |  2 +-
>   block/genhd.c           | 34 +++++++++++++++++++---------------
>   block/partitions/core.c |  3 +--
>   include/linux/genhd.h   |  6 ++++--
>   4 files changed, 25 insertions(+), 20 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
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hare@suse.de                              +49 911 74053 688
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Re: [dm-devel] [PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Martin K. Petersen]

Hi Christoph!

>  - If BLKROSET is used to set a whole-disk device read-only, any
>    partitions will end up in a read-only state until the user
>    explicitly clears the flag.

This no longer appears to be the case with your tweak.

It's very common for database folks to twiddle the read-only state of
block devices and partitions. I know that our users will find it very
counter-intuitive that setting /dev/sda read-only won't prevent writes
to /dev/sda1.

>  int bdev_read_only(struct block_device *bdev)
>  {
>  	if (!bdev)
>  		return 0;
> -	return bdev->bd_read_only;
> +	return bdev->bd_read_only ||
> +		test_bit(GD_READ_ONLY, &bdev->bd_disk->state);
>  }

I suggest doing bd->bd_read_only || get_disk_ro(...) here. That does
take part0 into account.

>  static inline int get_disk_ro(struct gendisk *disk)
>  {
> -	return disk->part0->bd_read_only;
> +	return disk->part0->bd_read_only ||
> +		test_bit(GD_READ_ONLY, &disk->state);
>  }
>  
>  extern void disk_block_events(struct gendisk *disk);

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Re: [dm-devel] [PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Christoph Hellwig]

On Wed, Dec 02, 2020 at 11:04:33PM -0500, Martin K. Petersen wrote:
> 
> Hi Christoph!
> 
> >  - If BLKROSET is used to set a whole-disk device read-only, any
> >    partitions will end up in a read-only state until the user
> >    explicitly clears the flag.
> 
> This no longer appears to be the case with your tweak.

True.

> 
> It's very common for database folks to twiddle the read-only state of
> block devices and partitions. I know that our users will find it very
> counter-intuitive that setting /dev/sda read-only won't prevent writes
> to /dev/sda1.

What I'm worried about it is that this would be a huge change from the
historic behavior.

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Re: [dm-devel] [PATCH 1/4] block: add a hard-readonly flag to struct gendisk

[Martin K. Petersen]

Christoph,

>> It's very common for database folks to twiddle the read-only state of
>> block devices and partitions. I know that our users will find it very
>> counter-intuitive that setting /dev/sda read-only won't prevent
>> writes to /dev/sda1.
>
> What I'm worried about it is that this would be a huge change from the
> historic behavior.

But that's what my users complained about and what the patch tried to
address.

Also, the existing behavior is inconsistent in the sense that doing:

# blockdev --setro /dev/sda
# echo foo > /dev/sda1

permits writes. But:

# blockdev --setro /dev/sda
<something triggers revalidate>
# echo foo > /dev/sda1

doesn't.

And a subsequent:

# blockdev --setrw /dev/sda
# echo foo > /dev/sda1

doesn't work either since sda1's read-only policy has been inherited
from the whole-disk device.

You need to do:

# blockdev --rereadpt

after setting the whole-disk device rw to effectuate the same change on
the partitions, otherwise they are stuck being read-only indefinitely.

However, setting the read-only policy on a partition does *not* require
the revalidate step. As a matter of fact, doing the revalidate will blow
away the policy setting you just made.

So the user needs to take different actions depending on whether they
are trying to read-protect a whole-disk device or a partition. Despite
using the same ioctl. That is really confusing.

The intent of my patch was to ensure that:

 - Hardware-initiated read-only state changes would not alter the user's
   whole-disk or partition policy settings.

 - Setting a policy on the whole-disk device would prevent writes to the
   whole device as the user clearly intended.

I have lost count how many times our customers have had data clobbered
because of ambiguity of the existing whole-disk device policy. The
current behavior violates the principle of least surprise by letting the
user think they write protected the whole disk when they actually
didn't.

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[dm-devel] [PATCH 2/4] rbd: remove the ->set_read_only method

[Christoph Hellwig]

Now that the hardware read-only state can't be changed by the BLKROSET
ioctl, the code in this method is not required anymore.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/rbd.c | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 2ed79b09439a82..2c64ca15ca079f 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -692,29 +692,10 @@ static void rbd_release(struct gendisk *disk, fmode_t mode)
 	put_device(&rbd_dev->dev);
 }
 
-static int rbd_set_read_only(struct block_device *bdev, bool ro)
-{
-	struct rbd_device *rbd_dev = bdev->bd_disk->private_data;
-
-	/*
-	 * Both images mapped read-only and snapshots can't be marked
-	 * read-write.
-	 */
-	if (!ro) {
-		if (rbd_is_ro(rbd_dev))
-			return -EROFS;
-
-		rbd_assert(!rbd_is_snap(rbd_dev));
-	}
-
-	return 0;
-}
-
 static const struct block_device_operations rbd_bd_ops = {
 	.owner			= THIS_MODULE,
 	.open			= rbd_open,
 	.release		= rbd_release,
-	.set_read_only		= rbd_set_read_only,
 };
 
 /*
-- 
2.29.2

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Re: [dm-devel] [PATCH 2/4] rbd: remove the ->set_read_only method

[Hannes Reinecke]

On 11/29/20 7:19 PM, Christoph Hellwig wrote:
> Now that the hardware read-only state can't be changed by the BLKROSET
> ioctl, the code in this method is not required anymore.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/block/rbd.c | 19 -------------------
>   1 file changed, 19 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
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[dm-devel] [PATCH 3/4] nvme: allow revalidate to set a namespace read-only

[Christoph Hellwig]

Unconditionally call set_disk_ro now that it only updates the hardware
state.  This allows to properly set up the Linux devices read-only when
the controller turns a previously writable namespace read-only.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index bc89e8659c403f..2442f43a1a5624 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2047,8 +2047,7 @@ static void nvme_update_disk_info(struct gendisk *disk,
 	nvme_config_discard(disk, ns);
 	nvme_config_write_zeroes(disk, ns);
 
-	if (id->nsattr & NVME_NS_ATTR_RO)
-		set_disk_ro(disk, true);
+	set_disk_ro(disk, id->nsattr & NVME_NS_ATTR_RO);
 }
 
 static inline bool nvme_first_scan(struct gendisk *disk)
-- 
2.29.2

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Re: [dm-devel] [PATCH 3/4] nvme: allow revalidate to set a namespace read-only

[Chaitanya Kulkarni]

On 11/29/20 10:22, Christoph Hellwig wrote:
> Unconditionally call set_disk_ro now that it only updates the hardware
> state.  This allows to properly set up the Linux devices read-only when
> the controller turns a previously writable namespace read-only.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>




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Re: [dm-devel] [PATCH 3/4] nvme: allow revalidate to set a namespace read-only

[Hannes Reinecke]

On 11/29/20 7:19 PM, Christoph Hellwig wrote:
> Unconditionally call set_disk_ro now that it only updates the hardware
> state.  This allows to properly set up the Linux devices read-only when
> the controller turns a previously writable namespace read-only.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/nvme/host/core.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
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[dm-devel] [PATCH 4/4] dm: use bdev_read_only to check if a device is read-only

[Christoph Hellwig]

dm-thin and dm-cache also work on partitions, so use the proper
interface to check if the device is read-only.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/md/dm-cache-metadata.c | 2 +-
 drivers/md/dm-thin-metadata.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index af6d4f898e4c1d..89a73204dbf47f 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -449,7 +449,7 @@ static int __check_incompat_features(struct cache_disk_superblock *disk_super,
 	/*
 	 * Check for read-only metadata to skip the following RDWR checks.
 	 */
-	if (get_disk_ro(cmd->bdev->bd_disk))
+	if (bdev_read_only(cmd->bdev))
 		return 0;
 
 	features = le32_to_cpu(disk_super->compat_ro_flags) & ~DM_CACHE_FEATURE_COMPAT_RO_SUPP;
diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 6ebb2127f3e2e0..e75b20480e460e 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -636,7 +636,7 @@ static int __check_incompat_features(struct thin_disk_superblock *disk_super,
 	/*
 	 * Check for read-only metadata to skip the following RDWR checks.
 	 */
-	if (get_disk_ro(pmd->bdev->bd_disk))
+	if (bdev_read_only(pmd->bdev))
 		return 0;
 
 	features = le32_to_cpu(disk_super->compat_ro_flags) & ~THIN_FEATURE_COMPAT_RO_SUPP;
-- 
2.29.2

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Re: [dm-devel] [PATCH 4/4] dm: use bdev_read_only to check if a device is read-only

[Hannes Reinecke]

On 11/29/20 7:19 PM, Christoph Hellwig wrote:
> dm-thin and dm-cache also work on partitions, so use the proper
> interface to check if the device is read-only.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/md/dm-cache-metadata.c | 2 +-
>   drivers/md/dm-thin-metadata.c  | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
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