linux-kernel - [PATCH AUTOSEL 5.15 4/6] s390/cio: Fix CHPID "configure" attribute caching

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Message-Id: <20250218202848.3593863-4-sashal@kernel.org>
Date: Tue, 18 Feb 2025 15:28:45 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>,
	Vineeth Vijayan <vneethv@...ux.ibm.com>,
	Eric Farman <farman@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Sasha Levin <sashal@...nel.org>,
	hca@...ux.ibm.com,
	agordeev@...ux.ibm.com,
	linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 4/6] s390/cio: Fix CHPID "configure" attribute caching

From: Peter Oberparleiter <oberpar@...ux.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@...ux.ibm.com>
Reviewed-by: Eric Farman <farman@...ux.ibm.com>
Tested-by: Eric Farman <farman@...ux.ibm.com>
Signed-off-by: Peter Oberparleiter <oberpar@...ux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.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);
 
-- 
2.39.5