Patch "s390/dasd: protect device queue against concurrent access" has been added to the 4.14-stable tree

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

    s390/dasd: protect device queue against concurrent access

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-dasd-protect-device-queue-against-concurrent-access.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@xxxxxxxxxxxxxxx> know about it.


>From db46cd1e0426f52999d50fa72cfa97fa39952885 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20H=C3=B6ppner?= <hoeppner@xxxxxxxxxxxxx>
Date: Wed, 25 Oct 2023 15:24:37 +0200
Subject: s390/dasd: protect device queue against concurrent access
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Jan Höppner <hoeppner@xxxxxxxxxxxxx>

commit db46cd1e0426f52999d50fa72cfa97fa39952885 upstream.

In dasd_profile_start() the amount of requests on the device queue are
counted. The access to the device queue is unprotected against
concurrent access. With a lot of parallel I/O, especially with alias
devices enabled, the device queue can change while dasd_profile_start()
is accessing the queue. In the worst case this leads to a kernel panic
due to incorrect pointer accesses.

Fix this by taking the device lock before accessing the queue and
counting the requests. Additionally the check for a valid profile data
pointer can be done earlier to avoid unnecessary locking in a hot path.

Cc:  <stable@xxxxxxxxxxxxxxx>
Fixes: 4fa52aa7a82f ("[S390] dasd: add enhanced DASD statistics interface")
Reviewed-by: Stefan Haberland <sth@xxxxxxxxxxxxx>
Signed-off-by: Jan Höppner <hoeppner@xxxxxxxxxxxxx>
Signed-off-by: Stefan Haberland <sth@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20231025132437.1223363-3-sth@xxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/s390/block/dasd.c |   24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -721,18 +721,20 @@ static void dasd_profile_start(struct da
 	 * we count each request only once.
 	 */
 	device = cqr->startdev;
-	if (device->profile.data) {
-		counter = 1; /* request is not yet queued on the start device */
-		list_for_each(l, &device->ccw_queue)
-			if (++counter >= 31)
-				break;
-	}
+	if (!device->profile.data)
+		return;
+
+	spin_lock(get_ccwdev_lock(device->cdev));
+	counter = 1; /* request is not yet queued on the start device */
+	list_for_each(l, &device->ccw_queue)
+		if (++counter >= 31)
+			break;
+	spin_unlock(get_ccwdev_lock(device->cdev));
+
 	spin_lock(&device->profile.lock);
-	if (device->profile.data) {
-		device->profile.data->dasd_io_nr_req[counter]++;
-		if (rq_data_dir(req) == READ)
-			device->profile.data->dasd_read_nr_req[counter]++;
-	}
+	device->profile.data->dasd_io_nr_req[counter]++;
+	if (rq_data_dir(req) == READ)
+		device->profile.data->dasd_read_nr_req[counter]++;
 	spin_unlock(&device->profile.lock);
 }
 


Patches currently in stable-queue which might be from hoeppner@xxxxxxxxxxxxx are

queue-4.14/s390-dasd-protect-device-queue-against-concurrent-access.patch



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