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 1097e76982a5d..6b0f1b8bf2790 100644 --- a/drivers/s390/cio/chp.c +++ b/drivers/s390/cio/chp.c @@ -661,7 +661,8 @@ 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);