Re: [PATCH] scsi: sd: block: Handle cases where devices come online read-only

On 2/8/19 6:38 PM, 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 have no way to distinguish between a user decision to set a block_device read-only and the disk being write protected as a result of the hardware state.

To overcome this we add a third state to the gendisk read-only policy. This flag is exlusively used when the user forces a struct block_device read-only via BLKROSET. We currently don't allow switching ro state in sysfs so the ioctl is the only entry point for this new state.

In set_disk_ro() we check whether the user override flag is in effect for a disk before changing read-only state based on the device settings. This means that devices that have a delay before going read-write will now be able to clear the read-only state. And devices where the admin or udev has forced the disk read-only will not cause the gendisk policy to reflect the mode reported by the 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

---

I have verified that get_disk_ro() and bdev_read_only() callers all handle the additional value correctly. Same is true for "ro" in sysfs.

Note that per-partition ro settings are lost on revalidate. This has been broken for at least a decade and it will require major surgery to fix. To my knowledge nobody has complained about being unable to make partition read-only settings stick through a revalidate. So hopefully this patch will suffice as a simple fix for stable.

---

Oof, my apologies for this regression. This looks like nice, tidy way to fix it.

block/genhd.c | 13 ++++++++++++- block/ioctl.c | 3 ++- drivers/scsi/sd.c | 4 +--- include/linux/genhd.h | 6 ++++++ 4 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c index 1dd8fd6613b8..e29805bfa989 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -1549,11 +1549,22 @@ void set_disk_ro(struct gendisk *disk, int flag) struct disk_part_iter piter; struct hd_struct *part;

• /*

• * If the user has forced disk read-only with BLKROSET, ignore
  

• * any device state change requested by the driver.
  

• */
  

• if (disk->part0.policy == DISK_POLICY_USER_WRITE_PROTECT)

• return;
  

I noticed drivers/s390/block/dasd_ioctl.c calls set_disk_ro() to set the policy, where-as the policy is set with set_device_ro() in the generic ioctl.

It's not setting the policy to DISK_POLICY_USER_WRITE_PROTECT so I think it would only be a problem if the user set it to 2 instead of 1 assuming any truthy value is acceptable. Then the user wouldn't be able to mark the disk as writable again since this would be true. Perhaps it's a somewhat far-fetched scenario.

if (disk->part0.policy != flag) { set_disk_ro_uevent(disk, flag); disk->part0.policy = flag; }

• /*

• * If set_disk_ro() is called from revalidate, all partitions
  

• * have already been dropped at this point and thus any
  

• * per-partition user setting lost. Each partition will
  

• * inherit part0 policy when subsequently re-added.
  

• */
  

  disk_part_iter_init(&piter, disk, DISK_PITER_INCL_EMPTY); while ((part = disk_part_iter_next(&piter))) part->policy = flag;

diff --git a/block/ioctl.c b/block/ioctl.c index 4825c78a6baa..16c42e1b18c8 100644 --- a/block/ioctl.c +++ b/block/ioctl.c @@ -451,7 +451,8 @@ static int blkdev_roset(struct block_device *bdev, fmode_t mode, return ret; if (get_user(n, (int __user *)arg)) return -EFAULT;

• set_device_ro(bdev, n);

• set_device_ro(bdev, n ? DISK_POLICY_USER_WRITE_PROTECT :

•       DISK_POLICY_WRITABLE);
  

  return 0; }

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index b2da8a00ec33..9aa409b38765 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..2bef434d4dff 100644 --- a/include/linux/genhd.h +++ b/include/linux/genhd.h @@ -150,6 +150,12 @@ enum { DISK_EVENT_EJECT_REQUEST = 1 << 1, /* eject requested */ }; +enum {

• DISK_POLICY_WRITABLE = 0, /* Default */
• DISK_POLICY_DEVICE_WRITE_PROTECT = 1, /* Set by device driver */
• DISK_POLICY_USER_WRITE_PROTECT = 2, /* Set via BLKROSET */

+};

• struct disk_part_tbl { struct rcu_head rcu_head; int len;