linvdimm, pmem: Preserve read-only setting for pmem devices

The pmem driver does not honor a forced read-only setting for very long:
	$ blockdev --setro /dev/pmem0
	$ blockdev --getro /dev/pmem0
	1

followed by various commands like these:
	$ blockdev --rereadpt /dev/pmem0
	or
	$ mkfs.ext4 /dev/pmem0

results in this in the kernel serial log:
	 nd_pmem namespace0.0: region0 read-write, marking pmem0 read-write

with the read-only setting lost:
	$ blockdev --getro /dev/pmem0
	0

That's from bus.c nvdimm_revalidate_disk(), which always applies the
setting from nd_region (which is initially based on the ACPI NFIT
NVDIMM state flags not_armed bit).

In contrast, commit 20bd1d026aac ("scsi: sd: Keep disk read-only when
re-reading partition") fixed this issue for SCSI devices to preserve
the previous setting if it was set to read-only.

This patch modifies bus.c to preserve any previous read-only setting.
It also eliminates the kernel serial log print except for cases where
read-write is changed to read-only, so it doesn't print read-only to
read-only non-changes.

Cc: <stable@vger.kernel.org>
Fixes: 581388209405 ("libnvdimm, nfit: handle unarmed dimms, mark namespaces read-only")
Signed-off-by: Robert Elliott <elliott@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
index a64023690cad..b9e0d30e317a 100644
--- a/drivers/nvdimm/bus.c
+++ b/drivers/nvdimm/bus.c
@@ -566,14 +566,18 @@ int nvdimm_revalidate_disk(struct gendisk *disk)
 {
         struct device *dev = disk_to_dev(disk)->parent;
         struct nd_region *nd_region = to_nd_region(dev->parent);
-        const char *pol = nd_region->ro ? "only" : "write";
+        int disk_ro = get_disk_ro(disk);
 
-        if (nd_region->ro == get_disk_ro(disk))
+        /*
+         * Upgrade to read-only if the region is read-only preserve as
+         * read-only if the disk is already read-only.
+         */
+        if (disk_ro || nd_region->ro == disk_ro)
                 return 0;
 
-        dev_info(dev, "%s read-%s, marking %s read-%s\n",
-                        dev_name(&nd_region->dev), pol, disk->disk_name, pol);
-        set_disk_ro(disk, nd_region->ro);
+        dev_info(dev, "%s read-only, marking %s read-only\n",
+                        dev_name(&nd_region->dev), disk->disk_name);
+        set_disk_ro(disk, 1);
 
         return 0;