Patch "s390/zcrypt: Fix wrong comparison leading to strange load balancing" has been added to the 4.14-stable tree

Patch "s390/zcrypt: Fix wrong comparison leading to strange load balancing" has been added to the 4.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    s390/zcrypt: Fix wrong comparison leading to strange load balancing

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     s390-zcrypt-fix-wrong-comparison-leading-to-strange-load-balancing.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Feb  1 13:45:42 CET 2018
From: Harald Freudenberger <freude@linux.vnet.ibm.com>
Date: Fri, 17 Nov 2017 16:32:22 +0100
Subject: s390/zcrypt: Fix wrong comparison leading to strange load balancing

From: Harald Freudenberger <freude@linux.vnet.ibm.com>


[ Upstream commit 0b0882672640ced4deeebf84da0b88b6389619c4 ]

The function to decide if one zcrypt queue is better than
another one compared two pointers instead of comparing the
values where the pointers refer to. So within the same
zcrypt card when load of each queue was equal just one queue
was used. This effect only appears on relatively lite load,
typically with one thread applications.

This patch fixes the wrong comparison and now the counters
show that requests are balanced equally over all available
queues within the cards.

There is no performance improvement coming with this fix.
As long as the queue depth for an APQN queue is not touched,
processing is not faster when requests are spread over
queues within the same card hardware. So this fix only
beautifies the lszcrypt counter printouts.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/s390/crypto/zcrypt_api.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/s390/crypto/zcrypt_api.c
+++ b/drivers/s390/crypto/zcrypt_api.c
@@ -218,8 +218,8 @@ static inline bool zcrypt_queue_compare(
 	weight += atomic_read(&zq->load);
 	pref_weight += atomic_read(&pref_zq->load);
 	if (weight == pref_weight)
-		return &zq->queue->total_request_count >
-			&pref_zq->queue->total_request_count;
+		return zq->queue->total_request_count >
+			pref_zq->queue->total_request_count;
 	return weight > pref_weight;
 }
 


Patches currently in stable-queue which might be from freude@linux.vnet.ibm.com are

queue-4.14/s390-zcrypt-fix-wrong-comparison-leading-to-strange-load-balancing.patch