Patch "s390/cio: fix race condition during online processing" has been added to the 6.6-stable tree

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

    s390/cio: fix race condition during online processing

to the 6.6-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-cio-fix-race-condition-during-online-processing.patch
and it can be found in the queue-6.6 subdirectory.

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



commit 57ffb8b547770a10e9f06dcc5e6ca80f163cf326
Author: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
Date:   Wed Apr 10 11:46:19 2024 +0200

    s390/cio: fix race condition during online processing
    
    [ Upstream commit 2d8527f2f911fab84aec04df4788c0c23af3df48 ]
    
    A race condition exists in ccw_device_set_online() that can cause the
    online process to fail, leaving the affected device in an inconsistent
    state. As a result, subsequent attempts to set that device online fail
    with return code ENODEV.
    
    The problem occurs when a path verification request arrives after
    a wait for final device state completed, but before the result state
    is evaluated.
    
    Fix this by ensuring that the CCW-device lock is held between
    determining final state and checking result state.
    
    Note that since:
    
    commit 2297791c92d0 ("s390/cio: dont unregister subchannel from child-drivers")
    
    path verification requests are much more likely to occur during boot,
    resulting in an increased chance of this race condition occurring.
    
    Fixes: 2297791c92d0 ("s390/cio: dont unregister subchannel from child-drivers")
    Reviewed-by: Alexandra Winter <wintera@xxxxxxxxxxxxx>
    Reviewed-by: Vineeth Vijayan <vneethv@xxxxxxxxxxxxx>
    Signed-off-by: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
    Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/s390/cio/device.c b/drivers/s390/cio/device.c
index 4ca5adce91079..57e0050dbaa53 100644
--- a/drivers/s390/cio/device.c
+++ b/drivers/s390/cio/device.c
@@ -363,10 +363,8 @@ int ccw_device_set_online(struct ccw_device *cdev)
 
 	spin_lock_irq(cdev->ccwlock);
 	ret = ccw_device_online(cdev);
-	spin_unlock_irq(cdev->ccwlock);
-	if (ret == 0)
-		wait_event(cdev->private->wait_q, dev_fsm_final_state(cdev));
-	else {
+	if (ret) {
+		spin_unlock_irq(cdev->ccwlock);
 		CIO_MSG_EVENT(0, "ccw_device_online returned %d, "
 			      "device 0.%x.%04x\n",
 			      ret, cdev->private->dev_id.ssid,
@@ -375,7 +373,12 @@ int ccw_device_set_online(struct ccw_device *cdev)
 		put_device(&cdev->dev);
 		return ret;
 	}
-	spin_lock_irq(cdev->ccwlock);
+	/* Wait until a final state is reached */
+	while (!dev_fsm_final_state(cdev)) {
+		spin_unlock_irq(cdev->ccwlock);
+		wait_event(cdev->private->wait_q, dev_fsm_final_state(cdev));
+		spin_lock_irq(cdev->ccwlock);
+	}
 	/* Check if online processing was successful */
 	if ((cdev->private->state != DEV_STATE_ONLINE) &&
 	    (cdev->private->state != DEV_STATE_W4SENSE)) {




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