[PATCH 5.4 029/154] s390/cio: Fix CHPID "configure" attribute caching

Greg Kroah-Hartman
2025-04-08T12:04:44Z

From: Peter Oberparleiter <oberpar@linux.ibm.com>

[ Upstream commit 32ae4a2992529e2c7934e422035fad1d9b0f1fb5 ]

In some environments, the SCLP firmware interface used to query a
CHPID's configured state is not supported. On these environments,
rapidly reading the corresponding sysfs attribute produces inconsistent
results:

$ cat /sys/devices/css0/chp0.00/configure
cat: /sys/devices/css0/chp0.00/configure: Operation not supported
$ cat /sys/devices/css0/chp0.00/configure
3

This occurs for example when Linux is run as a KVM guest. The
inconsistency is a result of CIO using cached results for generating
the value of the "configure" attribute while failing to handle the
situation where no data was returned by SCLP.

Fix this by not updating the cache-expiration timestamp when SCLP
returns no data. With the fix applied, the system response is
consistent:

$ cat /sys/devices/css0/chp0.00/configure
cat: /sys/devices/css0/chp0.00/configure: Operation not supported
$ cat /sys/devices/css0/chp0.00/configure
cat: /sys/devices/css0/chp0.00/configure: Operation not supported

Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Tested-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/s390/cio/chp.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/cio/chp.c b/drivers/s390/cio/chp.c
index 1fd982b4d64bd..18b2fc50463ba 100644
--- a/drivers/s390/cio/chp.c
+++ b/drivers/s390/cio/chp.c
@@ -646,7 +646,8 @@ static int info_update(void)
if (time_after(jiffies, chp_info_expires)) {
/* Data is too old, update. */
rc = sclp_chp_read_info(&chp_info);
- chp_info_expires = jiffies + CHP_INFO_UPDATE_INTERVAL ;
+ if (!rc)
+ chp_info_expires = jiffies + CHP_INFO_UPDATE_INTERVAL;
}
mutex_unlock(&info_lock);

--
2.39.5