From: Peter Oberparleiter Date: Fri, 31 Jan 2025 11:02:55 +0000 (+0100) Subject: s390/cio: Fix CHPID "configure" attribute caching X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=32ae4a2992529e2c7934e422035fad1d9b0f1fb5;p=linux.git s390/cio: Fix CHPID "configure" attribute caching 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 Reviewed-by: Eric Farman Tested-by: Eric Farman Signed-off-by: Peter Oberparleiter Signed-off-by: Vasily Gorbik --- diff --git a/drivers/s390/cio/chp.c b/drivers/s390/cio/chp.c index 4a0b3f19bd8e..4f01b1929240 100644 --- a/drivers/s390/cio/chp.c +++ b/drivers/s390/cio/chp.c @@ -695,7 +695,8 @@ 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);