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Subject[PATCH AUTOSEL 4.19 76/84] s390/dasd/cio: Interpret ccw_device_get_mdc return value correctly
Date
From: Jan Höppner <hoeppner@linux.ibm.com>

[ Upstream commit dd4b3c83b9efac10d48a94c61372119fc555a077 ]

The max data count (mdc) is an unsigned 16-bit integer value as per AR
documentation and is received via ccw_device_get_mdc() for a specific
path mask from the CIO layer. The function itself also always returns a
positive mdc value or 0 in case mdc isn't supported or couldn't be
determined.

Though, the comment for this function describes a negative return value
to indicate failures.

As a result, the DASD device driver interprets the return value of
ccw_device_get_mdc() incorrectly. The error case is essentially a dead
code path.

To fix this behaviour, check explicitly for a return value of 0 and
change the comment for ccw_device_get_mdc() accordingly.

This fix merely enables the error code path in the DASD functions
get_fcx_max_data() and verify_fcx_max_data(). The actual functionality
stays the same and is still correct.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Acked-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/s390/block/dasd_eckd.c | 9 +++++----
drivers/s390/cio/device_ops.c | 2 +-
2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index f89f9d02e788..108fb1c77e1d 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -1135,7 +1135,8 @@ static u32 get_fcx_max_data(struct dasd_device *device)
{
struct dasd_eckd_private *private = device->private;
int fcx_in_css, fcx_in_gneq, fcx_in_features;
- int tpm, mdc;
+ unsigned int mdc;
+ int tpm;

if (dasd_nofcx)
return 0;
@@ -1149,7 +1150,7 @@ static u32 get_fcx_max_data(struct dasd_device *device)
return 0;

mdc = ccw_device_get_mdc(device->cdev, 0);
- if (mdc < 0) {
+ if (mdc == 0) {
dev_warn(&device->cdev->dev, "Detecting the maximum supported data size for zHPF requests failed\n");
return 0;
} else {
@@ -1160,12 +1161,12 @@ static u32 get_fcx_max_data(struct dasd_device *device)
static int verify_fcx_max_data(struct dasd_device *device, __u8 lpm)
{
struct dasd_eckd_private *private = device->private;
- int mdc;
+ unsigned int mdc;
u32 fcx_max_data;

if (private->fcx_max_data) {
mdc = ccw_device_get_mdc(device->cdev, lpm);
- if ((mdc < 0)) {
+ if (mdc == 0) {
dev_warn(&device->cdev->dev,
"Detecting the maximum data size for zHPF "
"requests failed (rc=%d) for a new path %x\n",
diff --git a/drivers/s390/cio/device_ops.c b/drivers/s390/cio/device_ops.c
index 4435ae0b3027..f0cae1973f78 100644
--- a/drivers/s390/cio/device_ops.c
+++ b/drivers/s390/cio/device_ops.c
@@ -624,7 +624,7 @@ EXPORT_SYMBOL(ccw_device_tm_start_timeout);
* @mask: mask of paths to use
*
* Return the number of 64K-bytes blocks all paths at least support
- * for a transport command. Return values <= 0 indicate failures.
+ * for a transport command. Return value 0 indicates failure.
*/
int ccw_device_get_mdc(struct ccw_device *cdev, u8 mask)
{
--
2.20.1
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