[PATCH] device-dax: check devm_nsio_enable() return value

[Dan Williams]

If the dax_pmem driver is passed a resource that is already busy the
driver probe attempt should fail with a message like the following:

  dax_pmem dax0.1: could not reserve region [mem 0x100000000-0x11fffffff]

However, if we do not catch the error we crash for the obvious reason of
accessing memory that is not mapped.

 BUG: unable to handle kernel paging request at ffffc90020001000
 IP: [<ffffffff81496712>] __memcpy+0x12/0x20
 [..]
 Call Trace:
  [<ffffffff815c4960>] ? nsio_rw_bytes+0x60/0x180
  [<ffffffff815c6045>] nd_pfn_validate+0x75/0x320
  [<ffffffff815c63a9>] nvdimm_setup_pfn+0xb9/0x5d0
  [<ffffffff815c48ef>] ? devm_nsio_enable+0xff/0x110
  [<ffffffff815cb699>] dax_pmem_probe+0x59/0x260

Cc: <stable@xxxxxxxxxxxxxxx>
Fixes: ab68f2622136 ("/dev/dax, pmem: direct access to persistent memory")
Reported-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/dax/pmem.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
index 4a15fa5df98b..73c6ce93a0d9 100644
--- a/drivers/dax/pmem.c
+++ b/drivers/dax/pmem.c
@@ -78,7 +78,9 @@ static int dax_pmem_probe(struct device *dev)
 	nsio = to_nd_namespace_io(&ndns->dev);
 
 	/* parse the 'pfn' info block via ->rw_bytes */
-	devm_nsio_enable(dev, nsio);
+	rc = devm_nsio_enable(dev, nsio);
+	if (rc)
+		return rc;
 	altmap = nvdimm_setup_pfn(nd_pfn, &res, &__altmap);
 	if (IS_ERR(altmap))
 		return PTR_ERR(altmap);